The purpose of this study is to examine the relationship between stressful life events (SLE) and school engagement and to determine if there are some likely mediating variables between them. A sample of 1517 Chinese junior high school students (51.5% female) completed the adolescent self-rating life events checklist (ASLEC), Utrecht Work Engagement Scale-student (UWES-s), cognitive fusion questionnaire (CFQ), and positive psychological capital questionnaire (PPQ). The model was calculated using the PROCESS macro in SPSS. The serial mediator model revealed a significant negative effect of SLE on school engagement through psychological flexibility and psychological capital (effect = -0.08, 95% CI [-0.10, -0.06]). There was also a direct mediating effect through psychological capital (effect = -0.17, 95% CI [-0.21, -0.13]). The results of the present study may help to clarify mechanisms that might explain the association between SLE and school engagement. Future research on improving school engagement should consider the critical roles of psychological flexibility and psychological capital.