the credit card system has become an important part of China's financial electronization, which has profoundly changed people's financial concept and social payment system with its many characteristics such as quickness, convenience and security. Credit card business processing system mainly includes credit card exchange center, processing centers of issuing banks, savings outlets of banks, ATM outlets and POS systems. This paper mainly discusses the function of credit card exchange center. The credit card exchange center is connected with the following entities: the issuing bank processing center, the ATM／POS connected with the issuing bank, the remote credit card exchange center and the international credit card authorization network. First, the authorization transfer function authorization is simply the transaction license obtained by the cardholder from the issuing bank. The work done by the authorization processing system is to process the transaction request first (including information format conversion, information encryption and decryption, cardholder parameter check, agent processing, etc.), and then forward it to the transaction destination entity according to the transaction category, card number and information content, and ensure the integrity and effectiveness of the information. The authorization system of the credit card exchange center should provide the following authorization transfer situations: between the acquirer and the issuer, between the acquirer and the remote credit card exchange center or the national credit card exchange center, between the acquirer and the international authorization network, between the remote credit card exchange center or the national credit card exchange center and the issuer, between the international authorization network and the issuer, and between the ATM／POS machine directly connected to the credit card exchange center and the issuer. Authorized transfer between ATM/POS machines directly connected to credit card exchange centers and remote credit card exchange centers, and between ATM/POS machines directly connected to credit card exchange centers and international authorized networks. For example, the authorized transfer between the acquiring bank and the remote exchange center or the national credit card exchange center can be represented by the following figure. POS／ATM is an important means and tool for cardholders to obtain services by credit card, so it plays an important role in the whole credit card authorization service system. The POS/ATM machine can be directly connected to the credit card exchange center, or connected to the host computer of the bank POS/ATM system. The cardholder can also use the POS/ATM machine in different places, or use the POS/ATM machine abroad with a foreign exchange card. At this time, the authorization transfer process is completed by the POS/ATM authorization processing system. Generally speaking, the POS authorization processing system should support three kinds of cross-bank transaction functions: requesting authorization, revoking authorization and balance inquiry. The ATM authorization processing system should generally support the following inter-bank transaction functions: withdrawal, deposit and balance inquiry. Although their functions are different, the business process is basically the same, that is, the card is inserted into the ATM／POS machine to start the transaction, and the transaction request information sent out is transmitted to the information exchange center directly or through the credit card network, and the center will process the authorization request to a certain extent and then forward it to the issuing bank. The issuing bank checks and sends back the response information of authorization request to the exchange center, which sends it to ATM／POS through the original channel. After receiving the authorization response information, the relevant accepting bank sends a confirmation message to the exchange center, and the center sends the confirmation message back to the issuing bank. The switching center can also undertake the function of agent authorization. When the issuing bank is unable to handle authorization, for example, the issuing bank's host computer is out of order or doing routine maintenance work, the authorization request transmitted by the credit card exchange center cannot be received, or the network between the issuing bank and the exchange center is blocked, and the authorization request cannot reach the issuing bank, or the issuing bank exceeds the scheduled response time or the transaction amount is low-risk, etc., the credit card exchange center must be able to respond to authorization instead of the issuing bank, that is, authorize on behalf of the issuing bank. The agent authorization system can complete the functions of checking the payment stop list, approving or rejecting authorization according to the preset parameters of the issuing bank, processing by the issuing bank and checking the personal password. Authorization transfer is one of the most important functions of credit card exchange center, and it is also a key step in credit card business process. Second, the management function of stop payment list "stop payment list" is a risk management measure to protect the interests of cardholders, acquirers, card issuers and special merchants. Stop payment list management can be located in the issuing bank or exchange center, which provides tools for special merchants to identify lost cards, stolen cards or improper use of cards. The stop payment list regularly updates all the cardholders designated by the issuing bank to "receive the card" to a convenient file. The content of stop payment list management includes information such as card number, effective date, cancellation reason and action code. The credit card exchange center updates the stop payment list file at any time and sends the stop payment list to local banks and the national credit card exchange center. The credit card exchange center shall receive the payment stop list sent by card issuers, the National Credit Card Exchange Center and international credit card organizations, and merge it with the local payment stop list file immediately. The credit card exchange center will also send the stop payment list to local banks and the national credit card exchange center. The stop payment list must be sent to the bank regularly, and the effective date of the list will be indicated, and then the bank will print and distribute it to the special merchants. When the issuing bank updates the file of the city center, the city information center can send it to the national credit card exchange center immediately, so as to update the national stop payment list. The authorization system in the credit card exchange center should be able to directly check the files of the stop payment list in order to respond to the authorization requirements of those cards that have been included in the stop payment list. Iii. Clearing and Settlement System Function The credit card exchange center provides clearing services to banks in the region, and provides domestic and international clearing services to banks through cooperation with national credit card exchange centers, remote exchange centers and international credit card organizations. Liquidation generally consists of three continuous processes: sorting, settlement and fund allocation. First of all, banks extract transaction data, that is, the business data of other banks are transmitted to the credit card exchange center at a specified time, and the center verifies and confirms them, returns those substandard transactions, and then sorts them out, that is, the exchange center distributes the transaction data transmitted by the sending bank to the receiving bank and the credit card network in different places. Settlement is to determine the net difference of business data between banks participating in the exchange and generate a settlement report. After sorting, the center will merge the transaction data of local banks with the transaction data sent back by the remote network, count the net difference of each bank on that day, and provide the inter-bank fund transfer data to the local and remote payment systems (namely the clearing system of the People's Bank of China). Banks settle accounts through the People's Bank of China according to the daily net settlement data report provided by the Center. Banks negotiate with the People's Bank of China to carry out the actual capital operation between banks. IV. Risk Management Function A perfect credit card exchange center system should have a set of flexible and accurate risk management mechanism in line with the actual environment in addition to high-efficiency transaction processing function. The exchange center can collect all kinds of transaction data, so as to establish a comprehensive risk management system for anti-counterfeiting cards, anti-theft and forecasting suspicious merchants and cardholders by using the most advanced statistical model, and send relevant information to banks in time to prevent fraud and protect the interests of issuers, acquirers, special merchants and cardholders. The risk management function includes the following contents: (1) Card verification function: verify whether the credit card is a fake card, a fake card, or the magnetic tape data has been modified by password, so as to reduce the risks brought to the bank and protect the interests of cardholders and special merchants. (2) Personal password verification: it is mainly designed for transactions that need to use personal password (PIN), such as ATM or debit card transactions. After the exchange center performs PIN verification, the authorization requirements can be sent to the issuing bank or processed on behalf of the issuing bank according to the requirements of the issuing bank. (3) Statistics and forecast service of suspicious transactions: this is a risk monitoring service. With the help of the network, the exchange center compares the collected information about suspicious card holders with the data of clearing and settlement service, so as to identify the merchants who have accepted the transactions of these suspicious card holders, and then compares it with the "refusal" files in the system and the files of confirmed fraudulent transactions, so as to obtain a risk advance statement and send it to banks, so that banks can take action to prevent fraud. (4) Suspicious merchant inquiry service: The information exchange center should collect the information of all special merchants who have cheated in credit card transactions for banks, so that the acquiring bank can conveniently and quickly understand the credit background of the merchant when promoting the acquiring business to the merchant, so as to prevent it or not to sign a contract with it. V. Other functions The credit card exchange center provides log function, that is, it records all authorized transactions, system performance and files sent and received by banks, and makes statistics to estimate future demand. The transaction recorded by the exchange center can handle the disputed transaction. The exchange center also provides liquidation reports, risk management reports, service quality reports, business statistics reports, transaction inquiry reports, etc. In addition, the credit card exchange center can also consider adding some other additional functions. For example, it can provide card issuing services for banks that lack automated cards and processing systems, and it can also provide acquiring services for some banks to process transaction data sent back from special merchants and arrange liquidation on behalf of banks. The exchange center can also provide credit inquiry function. The center collects relevant information about credit of card holders of various card issuers, and provides inquiry service to the card issuers, so as to help the card issuers to evaluate the credit management of new card holders, repayment ability, etc. It can also provide credit card and business data to the government for reference by using the stored information. A fully functional and sound credit card exchange center is very important for the development of China's credit card system and plays a positive role in promoting the improvement of China's current payment system.