The intervention of bystanders plays a crucial role in mitigating incidents of school bullying. The decision of bystanders to intervene is influenced by factors stemming from both individual and environmental dimensions. Individuals with strong empathetic abilities may opt for passive observation rather than proactive intervention when confronted with bullying. This phenomenon prompts inquiry into whether environmental factors inadvertently constrain their interventionist tendencies. The five-step bystander intervention model provides a robust framework for understanding these dynamics. To examine the extent to which empathy and classroom bullying norms predicted each step of the bystander intervention model (i.e., Notice bullying events, Interpret as an emergency, Take Responsibility, Know how to intervene, and Act), this study conducted a questionnaire survey among 2054 Chinese adolescents (M[subscript age] = 13.87 years, 48.9% boys). Multilevel analyzes revealed that cognitive empathy predicted Interpret, Responsibility, Knowledge, and Action, and affective empathy predicted Interpret, Responsibility, and Action. Classroom bullying norms moderated the relationship between cognitive empathy and Responsibility. In classrooms with a higher bullying climate, greater cognitive empathy reduced students' perceived responsibility to intervene. Bystander intervention among adolescents in school bullying is determined by the interaction of individual characteristics and environmental factors. The findings support programs to encourage bystander intervention through empathy training and peer norms.