The difference between futures and stocks is that the life cycle of futures contracts is limited, and they will be delivered after the last trading day of the contracts. The futures market implements the position limit system. These two points are not only unfamiliar to investors in the securities market, but also extremely unaccustomed. For institutional investors, their investment is carefully planned, and the rules of stock index futures market and securities market are thoroughly studied before investment. Therefore, institutional investors' positions increase and decrease must conform to market rules. But for ordinary investors, the concept of main contract and the characteristics of main warehouse transfer are still worth introducing and explaining.

The so-called main contract refers to the contract with the largest position. Under normal circumstances, the contract with the largest position has the largest turnover. However, there will be such a short period of industrial futures every month. The trading volume of forward contracts with small positions is larger than that of main contracts, which leads to the phenomenon that forward contracts increase positions and main contracts decrease positions. This phenomenon is called warehouse transfer. It is worth pointing out that moving location is not literally "moving" or "migrating". Moving a position is the abbreviation of the process of closing a position in a recent contract and then opening a position in the same direction as the original position in a forward contract, which has transaction costs.

The main reason for moving positions is that futures contracts have the last trading day, and before the arrival of the last trading day, all undelivered positions must be closed gradually. Secondly, the margin of the exchange is gradually increased with the approach of the last trading day. Considering the efficiency of capital operation, the main force would rather gradually adjust the capital to a forward contract with lower margin. Third, the exchange not only began to adjust the margin before the delivery month 1 month, but also adjusted the required positions downwards.