The so-called stock index futures is a standardized futures contract based on a certain stock index. Buyers and sellers trade the stock index price level after a certain period of time. After the contract expires, the stock index futures will be delivered in the form of cash settlement. "Margin trading", also known as "securities credit trading", refers to the behavior of investors providing collateral to securities companies with Shenzhen Stock Exchange membership, borrowing funds to buy securities listed in this exchange or borrowing securities listed in this exchange and selling them. Including securities companies financing and securities lending to investors and financial institutions financing and securities lending to securities companies. The Securities Law before the amendment prohibited the securities credit transaction of margin financing and securities lending. Financing is to borrow money to buy securities, in layman's terms, to buy stocks! Securities companies borrow money from customers to buy securities, and customers repay the principal and interest at maturity. Customers buying securities from securities companies are called "short selling". Securities lending is to borrow securities to sell and then return them as securities. Securities companies lend securities to customers for sale, and customers return the same kind and quantity of securities at maturity and pay interest. Customers selling securities to securities companies are called "short selling". There are many obvious differences between stock index futures trading and stock trading: (1) Stock index futures contracts have an expiration date and cannot be held indefinitely. Under normal circumstances, the stock can be held all the time after buying, but the stock index futures contract has a clear expiration date. Therefore, trading stock index futures must pay attention to the contract expiration date to decide whether to close the position in advance or wait for the contract expiration for cash delivery. (2) Stock index futures trading adopts margin system, that is, when trading stock value futures, investors do not need to pay the full contract value, but only need to pay a certain proportion of funds as performance guarantee; At present, China's stock trading needs to pay the full value of the stock. Because stock index futures are margin trading, the loss may even exceed the investment principal, which is different from stock trading. (3) In the direction of trading, stock index futures trading can be short, can be bought before selling, or can be sold before buying, so stock index futures trading is a two-way transaction. However, in some countries, there is no short selling mechanism in the stock market, and stocks can only be bought first and then sold, and short selling is not allowed. At this time, stock trading is a one-way transaction. (4) In terms of settlement method, the stock index futures trading adopts the debt-free settlement system on the same day, and the exchange settles the trading margin on the same day. If the account margin is insufficient, it must be replenished within the specified time, otherwise it may be forced to close the position; However, stock trading adopts full amount trading, which does not require investors to add funds, and does not settle the book profit and loss after buying the stock but before selling it.