Whether invisible social capital can be used as a risk control mechanism to reduce the default risk of new agricultural business entities in agricultural credit guarantee financing and promote the sustainable development of agricultural credit guarantee system is an important issue worthy of attention and discussion.Based on the field survey data of new agricultural business entities in Shaanxi，Shanxi and Jiangsu provinces，this paper uses the Probit model to analyze the impact of social capital on the agricultural credit guarantee default of new agricultural business entities.The study finds that improving the social capitals of borrowers can effectively reduce their default risk in agricultural credit guarantee financing.Among them，rural social capital has the strongest effect，followed by government social capital，and financial social capital has the weakest effect.Heterogeneity analysis indicates that younger generations of new agricultural business entities are more susceptible to the effects of social capital in mitigating defaults.Additionally， agricultural guarantee institutions with smaller paid-in capital scales correlate with higher default risks， though social capital can partially offset this adverse impact.Mechanism analysis shows that enhancing the borrower’s willingness and ability to repay loans serves as a key pathway through which social capital reduces the default risk of new agricultural business entities in agricultural credit guarantee financing.These conclusions provide empirical basis and practical insights for promoting the social capital accumulation among new agricultural business entities and refining the risk control strategies for agricultural credit guarantee system.