Generally speaking, the main contract is the one with large trading volume, and it is more obvious when adding positions.

The main contract is the contract with the largest position. The reason for making this contract is that the transaction is more active and easier to close. The main contract is constantly changing, mainly because the expiration date of the contract is approaching, so it is necessary to move the position to the next month, so that the volume and position of the next month will increase rapidly.

Stock index futures are now changed once a month, and will be changed from IF 1209 to IF 12 10 in September, and so on.