Abstract: Joining cooperatives as an effective way for agricultural businesses to participate in market competition is not only an important measure for constructing a new type of agricultural management system, but also a proper meaning for building modern agriculture. For the new type of agricultural business-family farms, theoretically, the willingness and probability of family farms joining cooperatives will gradually increase with the expansion of their scale of operation. Therefore, the purpose of this paper is to empirically analyze the relationship between the scale of land management and the behavior of joining cooperatives of family farms. Considering the endogenous problems caused by the simultaneous relationship between land management scale and the behavior of joining cooperatives, this paper adopts the instrumental variable estimation method and the panel data of 795 farming family farms by the national family farm monitoring activities from 2014-2016 to analyze the behavior of joining cooperatives empirically. The estimation results show that the scale of land management for family farms has a significant positive effect on farms joining cooperatives, that is, the probability of farms with large scale of operations joining cooperatives is even higher; and even considering the exogenous effects of the number of cooperatives in the area of the family farms, this conclusion is still robust. Finally, the article gives the corresponding policy recommendations.