The reason why gamma will change from large to small: futures prices rise, the delta value of the long call option moves from 0 to 1, and the delta value of the long put option moves from -1 to 0, that is, the delta value of the option moves from small to For large movements, the gamma value is positive. When futures prices fall, the delta value of long call options moves from 1 to 0, and the delta value of long put options moves from 0 to -1, that is, the delta value of the option moves from large to small, and the Gamma value is negative.