Using a representative sample of 11760 Chinese students from the Program for InternationalStudent Assessment 2018 (PISA 2018) to investigated the relationship between academic performanceand school belonging of middle school students and the moderating role of competition environment.The result indicated that: Academic performance had a significant and positive predictive effect on schoolbelonging and competition environment moderated this relationship: in a low-level competitive schoolenvironment, academic performance had a significant and positive predictive effect on school belonging.But in a high-level competitive school environment, such effect was no longer significant. For schools, theneed for students to belong should be emphasized in order to promote their mental health.