Objective: A longitudinal mediating model was designed to explore the relationship between sleep chronotype and depressive mood with stressful life events as the mediating variable, so as to provide reference basis for preventing depression in adolescents. Methods: From March (T1) to October (T2) 2022, the Munich Chronotype Questionnaire, and Adolescent Self-rating Life Events Checklist and Center for Epidemiologic Studies Depression Scale were administered in 1 251 middle school students in the first and second grades of a middle school in Meishan, Sichuan Province for a follow up study. Two wave of date on sleep time type, stressful life events, and depressive moods were collected. Results: At T1, the detection rate of depressive mood was 22.5% in adolescents but 27.0% at T2.At the same time point, there were significant positive correlations between chronotype, stressful life events and depressive mood ( r=0.06-0.69, P <0.05). Cross lagged model results showed that early sleep chronotype could significantly predict later depressive mood ( β=0.53, P <0.05), and early depressive mood could significantly predict later sleep chronotype ( β=0.01, P <0.01). Longitudinal mediation model analysis showed that T1 sleep chronotype not only directly affected T2 depressive mood (direct effect value=1.421, 95% CI =0.985- 1.858 , P <0.01), but also affect T2 depressive mood through the partial mediating effects of T2 stressful life events (indirect effect value=1.268, 95% CI =0.810-1.726, P <0.05). Although T1 depressive mood was a direct predictor of T2 sleep chronotype (direct effect value=0.025, 95% CI =0.017-0.032), it was not a direct predictor of T2 sleep chronotype by partial intermediate action of T2 stressful life events (indirect effect value=-0.001, 95% CI = -0.006- 0.004, P >0.05). Conclusions Sleep chronotype can not only directly predict depressive mood of adolescents, but also indirectly affect depressive mood of adolescents through the longitudinal mediating effect of stressful life events. To prevent depression and improve mental health in this population, adolescents should develop the habit of early sleep schedule, and improve their ability to cope with stressful life events.