China is the big country with a large population and grain, so it is important for China to promote grain production and ensure food security. Because there exists the game behavior among various subjects of interest in the market, the purchasing price is decided by farmers and grain purchasing enterprises. Taking the Nash bargaining model as the bargaining process, using the data about the price of wheat from 2006 to 2014, this paper studies the bargaining power of farmers and enterprises in the process of grain purchase, in order to determine the policy effect of the minimum grain purchase price. The results show that the policy can really change the bargaining power of farmers and protect their interests, but the policy has implementation lags. More importantly, the policy will lead to a change in the bargaining power of farmers from absolute disadvantage to absolute advantage, resulting in the ability of farmers to obtain the dominant price at the lowest purchase price, that is, the policy distorts the market pricing mechanism. Finally, this paper gives the model and empirical conclusions and policy suggestions.