This paper introduces plastic model of material deformation theory to analysis on futures price in order to analyze mutation of the price. Taking corn futures for example, this paper, through building a variety of plastic models, finds that the coefficient of plastic examinations can pass smoothly, and existence of plastic in corn futures prices is also confirmed. Consequently, this paper chooses exponential function to build relationship between lock amount and futures prices so as to ananlyze their corresponding relations. Finally, this paper finds that when locked amount in the lowest point of the abnormal fluctuations returns to 0.8 on the occurrence of abnormal fluctuations in the amount of lock, there will have a mutation of the market price with price change in the absolute value of more than 5%.