The vitality of a policy lies in its implementation. In the rural society based on "relationship", village cadres with substantial discretion often adopt an informal "relationship governance" model to implement policies, and realize the constraint and incentive of each other's behavior through interpersonal emotional connection and reciprocal obligation. This study takes the grass-roots implementation of the river chief system policy as an example. By introducing the interactive adaptation theory of policy implementation, an executive model including human relationship, individual ability and service motivation is constructed. By using a total of 961 survey data collected by the research group in Jiangsu, Anhui and Shaanxi provinces, the comprehensive impact of relationship governance on the policy implementation ability of village cadres is empirically investigated. The results show that: Relationship governance will lead to the improvement of public acceptance of policies and the reduction of implementers' compliance with policies. Under the joint action of the two forces, there is an "inverted U-shaped" relationship between the degree of relationship governance and the policy implementation ability of village cadres. On the one hand, public leadership can enhance policy implementation, on the other hand, it can buffer the negative impact of relationship governance, and play a positive mediating role in the impact of relationship governance on policy implementation. Public service motivation is the boundary condition to improve public policy implementation. When village cadres have a higher level of public service motivation, the negative impact of relationship governance on policy implementation is weakened. Combined with the special situation of rural social field, this study expands the theory of policy implementation in the Chinese context, and can provide policy reference and theoretical guidance for the grass-roots policy implementation.