The study aimed to examine the impact of social-emotional competence (SEC) training for teachers on adolescents' SEC and to explore the underlying mechanisms. Based on the KAB behavior change model, this study constructs an analytical framework and empirically analyzes the intrinsic connection between teacher SEC training and students' SEC using data from 3,588 participants in the SSES project. The findings indicate that students taught by teachers with higher participation in SEC training achieved SEC scores that were 5.08 points higher on average than those taught by teachers with lower participation. Among the various aspects, teacher SEC training has the greatest impact on students' collaboration skills and the least impact on openness. Furthermore, the analysis of the mechanism through which teacher SEC training affects students' SEC reveals that this impact is statistically significant and is mediated by teachers' teaching attitudes and methods. While teacher SEC training has a significant impact on teachers' teaching methods, this impact is not unilaterally transmitted but is moderated by teacher-student relationships. The research results show that offering SEC training for teachers can positively impact students' SEC and highlight the important role of teachers' attitudes and methods in this process.