BackgroundThe role of rumination in depression remains controversial. We aimed to establish the ruminative tendency style theory (RTST), discuss the occurrence of depression in adolescents with rumination as the core, and explore the different associations between adolescent ruminative tendency, ruminative style, and depression. MethodsThis study employed an online questionnaire survey of 1110 Chinese adolescents aged 12–17 years, assessing ruminative tendency, ruminative style, stressful life events, depressive state, depressive trait, the Big Five personality traits, and social support. Conditional process analysis was used to test the chain mediation effect with Ruminative Style as a moderator. After screening for the predictor variables, a logistic regression risk prediction model was established and validated internally. ResultsThe chain mediation effect of ruminative tendency and depressive trait between stressful life events and depressive state was significant, with the indirect effect accounting for 63.4%. Ruminative Style negatively moderated the relationship between Ruminative Tendency and Depressive Trait (β=-0.053,P<0.001). The risk prediction model for depressive state showed good calibration and clinical utility. Area under the curve values for the validation and training sets were 0.926 and 0.927, respectively. ConclusionDifferent associations may exist between adolescent ruminative tendency, ruminative style, and depression, and the proposal of ruminative style is of great significance for intervention in adolescent depression.