The daily mark-to-market system of futures trading refers to the settlement system in which the settlement department calculates and checks the balance of the margin account after the daily closing, and keeps the margin balance above a certain level by issuing a notice of additional margin in time to prevent debt. In futures trading, some profits must come from the losses of the other party. However, the profit and loss settlement is not carried out directly between the two parties to the transaction, but is realized by the exchange by transferring the profits and losses in the margin accounts of both parties. When the loss-making party's funds in the margin account of the exchange cannot bear its losses (the margin balance is negative after deducting losses), the exchange, as the guarantor of the contract, must bear this part of the losses on its behalf to ensure that the profit-making party can get all the profits in time. In this way, the loss is convenient for defaulting on debts to the exchange. In order to prevent this debt phenomenon, daily mark-to-market and daily debt-free settlement system (referred to as daily mark-to-market system) came into being. After the end of each trading day, the settlement department of the exchange calculates the settlement price of the day according to the all-day trading, and accordingly calculates the floating profit and loss of each member's position and adjusts the available balance of the member's margin account. If the adjusted margin balance is lower than the maintenance margin, the exchange will issue a notice before the opening of the next trading day, requesting additional margin. If the member unit fails to add the margin on time, the transaction ownership will be forced to close the position. China's domestic futures settlement system is a daily mark-to-market system, also known as the daily debt-free settlement system. In fact, in China, the exchange first managed members' funds according to the financial system of general enterprises, and adopted the monthly settlement system, without the awareness of controlling risks. Losses arising from daily transactions should be treated as floating losses. It can be proved that once the market continues to develop in an unfavorable direction for investors, the accumulated daily losses are so large that the margin balance is lower than the prescribed level, there will be the risk of being tied or even defaulting. Stock index futures are marked to the market on a daily basis, that is, investors' profits and losses are settled after the settlement on the same day, and positions' profits and losses calculated at the settlement price on the same day are increased or decreased. It plays an important role in controlling the risk of stock index futures market and maintaining the normal operation of the market.

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