In “leading enterprise+farmer” cooperation model, farmer’s behavior of breaching contract exists generally. In this paper, from the angle of incomplete contract, the influencial factors of farmer breaking contract are analyzed. It is found that farmer sex, age, culture degree and farming period have obvious effects on the behavior of breaching contract. Under regulating effect of relationship quality, farmer assest specificity, exogenous uncertainty and endogenous uncertainty affect farmer’s breaking behavior. That is, the higher the farmer assest specificity, the lower the farmer breaching tendency; higher exogenous uncertainty causes that farmer is easy to generate breaching behavior; higher endogenous uncertainty causes that farmer is also easy to take breaching behavior.