Based on the perspective of social norms, this paper constructed the evaluation index system of social norms from the three dimensions of descriptive norms, imperative norms and personal norms, and based on the data of 1076 groups of farmers obtained from the actual survey, the binary Logit model was used to analyze the influencing factors of farmers’participation in the supply of small-scale farmland water conservancy facilities. Interpersonal trust, including family and friend trust, villager trust and general trust, was introduced as the mediating variable to explore the transmission path and mechanism of social norms influencing farmers’participation in small-scale farmland water conservancy supply. The results show that among social norms, descriptive norms and individual norms have a positive effect on farmers’participation in the supply behavior of small-scale farmland water conservancy facilities, while imperative norms have a negative effect. Social norms and interpersonal trust have positive effects on farmers’participation in small-scale farmland water conservancy supply behaviors, and social norms effect farmers’participation behaviors directly, while interpersonal trust can produce indirect effect.