The main contract is the contract with the most active position or volume. Because futures contracts are due for delivery, they cannot be held indefinitely. Futures players are mostly speculative, they just want to close their positions and make profits. So after the delivery, the speculators of this contract will turn to the next target contract. In this way, the positions of expired contracts have been greatly reduced, and the volume of transactions has declined rapidly. Those who are still holding positions are generally enterprises with hedging needs. The main contract conversion has no impact on the market. If you haven't left before the delivery month, your counterparty will gradually decrease. At this time, you will face the situation that the entrustment order cannot be closed or the transaction is slow.