Abstract: We recruited 1,631 middle and high school students to explore the relationship between personality traits and school bullying, and the moderated and mediating roles of self-concept and loneliness on this relationship. Statistical analysis was performed using SPSS 18.0. Results showed that (1) neuroticism had a significant positive predictive effect on being bullied, extroversion had a significant negative predictive effect on being bullied, and agreeableness had a significant negative predictive effect on bullying/being bullied; (2) loneliness played a mediating role between neuroticism and bullied behaviors, extroversion and bullying behaviors, and agreeableness and bullying/bullied behaviors; (3) self-concept played a moderating role on the mediation pathway of loneliness on neuroticism, extraversion, agreeableness and bullying behaviors. Therefore, to reduce the frequency of school bullying among adolescents, we should not only reduce their levels of loneliness but also improve their levels of self-concept. The prevention and treatment of school bullying is of great significance to the construction of a good family environment, campus environment and even social environment. This paper discusses the formation mechanism, influencing factors and development rules of school bullying behavior, in order to put forward scientific suggestions for the prevention and treatment of school bullying, and promote a good interpersonal relationship and a harmonious social environment. Moreover, this paper explores the internal relationship between personality traits, loneliness, self-concept and bullying, and further enriches the theories related to the influencing factors of bullying. Keywords: school bullying, personality traits, loneliness, self-concept, adolescents Hypotheses: We proposed hypothesis one: loneliness plays a mediating role in the relationship between personality traits and school bullying. We proposed hypothesis two: self-concept plays a moderating role in the mediation pathway for loneliness on the relationship between personality traits and school bullying. Analysis plan: First, the data were standardized. Second, the macro program PROCESS in SPSS was used to test the moderated mediating model. Finally, the deviation correction and the percentile Bootstrap method were set. The number of repeated sampling was set to 5,000 for inspection and the confidence interval (CI) was set to 95%. The test of the mediating effect was then conducted. We used Model 4 of the SPSS macro designed by Hayes (2012) controlling for gender and age to perform the mediating effect test of loneliness on the various personality trait dimensions.The test of the moderated mediation model was then performed. We established a moderated mediation model consisting of three personality trait dimensions (neuroticism, extraversion, and agreeableness) and school bullying/being bullied, in which we regarded loneliness as the mediating variable and self-concept as the moderating variable using the Model 14 of the SPSS macro designed by Hayes (2012). Project summary: The study specifically looked at each aspect of personality traits and their relationship with loneliness, self-concept, and school bullying. It also revealed the mediating effect of loneliness, regulating the effect of self-concept. It helped us to have a clear understanding of the generating mechanism of school bullying. From that, we could better prevent the occurrence of school bullying in the process of education and teaching：Reduce loneliness, and improve the level of self-concept among adolescents. Furthermore, our educators and parents should pay more attention to teenagers' interpersonal relationships and the inner world to facilitate their healthy growth.