Objective To explore the mediating role of self-esteem in the relationship between peer victimization and the frequency of non-suicidal self-injury （NSSI） in adolescents with depressive episode. Methods A total of 142 adolescents with depressive episode hospitalized in the Department of Pediatric Psychology of Suzhou Guangji Hospital from January to December 2021 were recruited as the research subjects. Functional Assessment of Self-Mutilation （FASM）， Rosenberg Self-Esteem Scale （RSES），Multidimensional Peer Victimization Scale （MPVS） and Patient Health Questionnaire-9 （PHQ-9） were applied to investigated NSSI behavior， self-esteem level， peer victimization and depression level of the patients. Spearman correlation was used to analyze the correlation between peer victimization， self-esteem and NSSI frequency in adolescent depressive patients. PROCESS 3.0 was used for mediation effect test. Results The detection rate of NSSI among adolescents with depressive episode was 76.8% （109/142）. The scores of PHQ-9， RSES and MPVS were （20.39±4.85）， 19.00 （14.75，23.00） and 16.00（4.00，32.00）， respectively， in NSSI group. The scores of peer victimization， physical victimization， verbal victimization， social manipulation and attacks on property were all positively correlated with NSSI frequency （r=0.432，0.303，0.407，0.387，0.278；P＜ 0.01）； while selfesteem was negatively correlated with NSSI frequency （r=-0.460，P ＜ 0.01）. The results of the intermediary test showed that self-esteem had a partial mediating effect between peer victimization and NSSI frequency， and the mediating effect accounted for 31.9%-60.2%. Conclusions The self-esteem has a partial mediating effect on the relationship between peer victimization and the frequency of NSSI in adolescents with depressive episode， suggesting that attention should be paid to peer victimization of adolescent depressive patients and the intervention of low self-esteem to reduce the occurrence of NSSI behavior.