Objective: To explore the relationship among grit, self-identity and self-esteem and the mediating role of self-identity between grit and self-esteemin middle school students, so as to provide evidence for the study of grit of middle school students. Methods: In March 2019,1 476 middle school students were selected from two ordinary middle schools in a county of Fujian Province. 12-Ttem Grit-scale, Selt-identity Scale and Selt-esteem Scale were used to conduct the questionnaire survey. Results: Relevant analysis showed that perseverance of efforts, consistency of interests were positively correlated with self-identity (r=0.40, 0.31,P<0.01) and self-esteem (r=0.46, 0.18, P<0.01). Self-identity and self-esteem were positively correlated (r=0.67,P<0.01).The results of the mediation test showed that self-identity partially mediates the relationship between perseverance of efforts and self-esteem,mediation effect accounted for 50.38% of the total effect.Self-identity fullymediatesthe relationshipbetween consistency of interests and self-esteem. Conclusion The self-identity of middle school students partially mediates the relationship between perseverance of efforts and self-esteem, and completely mediates the relationship between consistency of interests and self-esteem.