With the development of information technology, the functions of social networking sites are constantly enriched to meet people's various needs and increasingly favored by people. According to relevant survey data, the utilization rate of social networking sites in China has reached more than 90%, the largest proportion of the audience being young people aged 20 to 29, accounting for 30% of the total usage. Data from the 2015 research report on users' behavior of social networking apps in China shows that the proportion of minors using social networking sites covers almost 1/3 of the total, which indicates that the audience group is generally teenagers. A social networking site is like a double-edged sword. On one hand, People can use it to focus on the content they are interested in, learn about hot news, acquire and share knowledge, upload photos, update status, watch videos and listen to music, etc. However, if someone is immersed in it, it may adversely affect one's individual work, study, health, interpersonal relationship, and the like. In this study, 909 college students from a university in Jiangxi province were surveyed. According to the scores of the scale of overuse of social networking sites, 159 over users of social networking sites were selected as the research objects. The research tools are: social network overuse scale, social network use motive scale, life satisfaction scale, self-esteem scale and stress perception scale. The author made a comparative study of these college students' choices of social networking sites, involving mental health, use motive and other aspects. This paper will focus on the relationship among mental health, overuse of social networking sites and motive for social networking sites. Finally, the relationship among motive, mental health and overuse of social networking sites is discussed in order to provide factual evidence for research in related fields. The following conclusions are made: (1) According to the survey, in the current situation of the use of social networking sites, the general users account for more than 80%, and the rest nearly become over users. The motive for social networking sites and mental health variables have certain differences. In addition, the overuse group has higher motives for pastime, information acquisition, entertainment, self-expression, escape and stress- perceiving than the general group, but lower scores in life satisfaction and self-esteem than the general group. (2) In the study, there is a significant positive correlation between motives for pastime, information acquisition, entertainment, self-expression and escape from reality on social networking sites, and overuse. (3) There is a significant negative correlation between life satisfaction and overuse of social networking sites; self-esteem is not significantly correlated with overuse of social networking sites; there is a significant positive correlation between stress perception and overuse of social networking sites. (4) Life satisfaction has a significant moderating effect on motives for pastime, self-expression, escape and overuse of social networking sites, while the effect on motives for information acquisition and entertainment is not significant; (5) The moderating effect of self-esteem on motives for social networking sites and overuse of social networking sites is not significant; (6) Stress perception has a significant moderating effect on motives for entertainment and overuse of social networking sites, while the effect on motives for pastime, information acquisition, self-expression, escape and overuse of social networking sites is not significant. The study examines the factors of excessive use of social networking sites, especially for college students, the over user group, which can further increase college students' attention to this phenomenon, strengthen their awareness of self-protection, thus making them use social networking sites in a more restrained way; meanwhile, it helps for educators to provide effective intervention measures and corrective measures for over users of social networking sites according to students' psychological well-being and use motive.