Objective: To explore the buffering effect of positive childhood experiences (PCEs) on mental health risks among adolescents before and after COVID-19 epidemic. Methods: In October 2019 (before the outbreak of COVID-19), 1 322 students from grades 4 to 9 were recruited from primary and secondary schools in two counties of Chizhou city, Anhui Province. A questionnaire survey was conducted to collect general demographic information, PCEs, depressive symptoms, anxiety symptoms, self harm behavior, suicidal ideation. Follow up survey was conducted after school re opening (May 2020). Mental health status before and after the COVID-19 epidemic was compared among students with different PCEs by multiple logistic regression analyses. Results: The detection rates of depressive symptoms, anxiety symptoms, self harm behavior and suicidal ideation (22.6%, 16.0%, 40.0%, 29.9%) of the respondents after school re opening were significantly higher compared that before the epidemic (16.5%, 13.5%, 31.1 %, 22.6%). There were no significant differences in the detection rates of depressive symptoms, anxiety symptoms,self harm behavior and suicidal ideation between high PCEs group before and after the epidemic ( Z =-0.05,0.27,0.84,1.84, P >0.05). Multivariate Logistic regression analysis showed that the risk of depressive symptoms and self harm behavior in the low PCEs group after school re opening was 1.39 times higher than that before the epidemic (95% CI= 1.05 -1.84, P <0.05). The risk of non suicidal self injury behavior in the low PCEs group after school re opening was 1.31 times higher than that before the epidemic (95% CI= 1.05 -1.62, P <0.05). There were no significant differences in mental health detection rates in high PCEs group before and after the epidemic ( P >0.05). Conclusion During the time of COVID-19 epidemic, PCEs is associated with lower rates of depressive symptoms, anxiety symptoms, self harm behavior and suicide ideation in adolescents. The findings suggest that more support and help should be given to adolescents from the perspectives of family, school and peers, so as to reduce the adverse effects of public health emergencies on adolescents mental health.