Abstract: The farmers cooperative union is a product of the development of farmers cooperatives to a certain stage, and it is also an inevitable trend of the development of China’s farmers cooperatives. Based on a data of 614 farmers cooperatives in 12 counties and 8 provinces and applying the theory of strategic alliance and resource dependence, this paper analyzed the factors that affect farmers cooperatives to join the union. Results show that 14.5% of farmers cooperatives joined the union; and compared with the eastern region, the probability of farmers cooperatives in the central and western regions to join the union was lower. Joining the union is influenced by the status of intangible assets, the characteristics of the chairman and the external environment. Intangible assets and external environment have significant impacts on farmers cooperatives joining the union. Farmers cooperatives with resources such as sales channels and brands and being rated as model cooperatives tend to form a union, and the small-scale farmers cooperatives tend to join the union. Joining the union has an exemplary effect, the higher the proportion of farmers cooperatives joining the union in a region, the higher of the possibility of farmers cooperatives choosing to join the union. The age and the education level of the director have no significant impact on the farmers cooperatives joining the union. To promote the healthy development of China’s farmers cooperative union, the government should comply with the high quality development trend of farmers cooperatives, make full use of financial, tax and other policy tools to support the development of farmers cooperatives, increase the propaganda of related policies, and constantly improve the service capacity of the union.