PURPOSE: Although adolescent online behavior has become a research hotspot in recent years, most studies focus on the risks in online life, lacking research on positive phenomena online and even more so on the exploration of their internal mechanisms. This study explores the relationship between self-other overlap, empathy, moral identity, and adolescent online altruistic behavior, and discusses whether empathy and moral identity play a serial mediating role between self-other overlap and adolescent online altruistic behavior. PATIENTS AND METHODS: This study conducted a questionnaire survey on 392 adolescents. Descriptive analysis and correlation analysis were performed using SPSS 23.0, and model construction and bias-adjusted bootstrap mediation effect testing were conducted using Mplus 8.3. RESULTS: There were significant positive correlations between self-other overlap, empathy, moral identity and internet altruistic behavior (r=0.168~0.412, all p<
0.01). Self-other overlap can directly predict internet altruistic behavior, and can also indirectly predict internet altruistic behavior through chain mediating effects of empathy and moral identity. CONCLUSION: This study has discovered the internal mechanism by which self-other overlap affects online altruistic behavior, demonstrating that empathy and moral identity play a chain mediating role in this process. This finding can guide people to view the impact of network development more dialectically, calling for a focus on how to leverage the positive effects of the internet rather than simply blaming its negative impacts. It also provides new theoretical basis for guiding adolescents on how to use the internet healthily, contributing to the construction of a more harmonious online environment.