Abstract: In order to explore the influence of social network on the loneliness of university students and its mechanism，a sample of 964 university student were recruited for the study. They were required to complete a battery of questionnaires, including social networking questionnaire, online positive feedback questionnaire, social anxiety scale and loneliness scale. Results indicated that: the mediation analysis revealed that SNS use could affect loneliness through the mediation of online positive feedback and social anxiety. The mediation effect contained three paths: the separate mediation effect of online positive feedback, the separate mediation of social anxiety，and the serial mediation effect of online positive feedback and social anxiety. This study reveals the relationship between the use of social networking sites and loneliness and its mechanism, and deepens the research on the influence of social networking sites on individual mental health.