The peer-to-peer lending market has developed rapidly over the past decade and reveals a severe problem of information asymmetry. This research constructed a four-party evolutionary game model to analyze the influence pathway of the guarantee mechanism on the users’ participation of the peer-to-peer lending platform and conducted an empirical study applying the mediating effect model and simultaneous equation model based on data of China’s peer-to-peer lending platform. The theoretical model shows that the guarantee mechanism reduced the participation of borrowers of the peer-to-peer lending platform through a screening effect, but increased the participation of investors through a signal effect. In the case of the platform self-guarantee, there existed a self-screening effect, whose influence on the participation of investors depended on the strength of external constraints imposed on the platform enterprises. Further, the empirical study shows that during the sample period, the platform self-guarantee mechanism reduced the scale of borrowers and investors of the peer-to-peer lending platform at the same time, thus reducing the transaction volume of the platform. Although the third-party guarantee mechanism reduced the scale of borrowers, it increased the scale of investors, and the comprehensive effect was to increase the transaction volume of the platform. On this basis, this research puts forward suggestions such as strengthening the qualification examination of the platform enterprises, transforming the platform self-guarantee mechanism into the third-party guarantee mechanism, and introducing more signal mechanisms.