This study aims to explore the interrelationships between teacher competence, college students' mental health, and academic achievement, and to analyze the mediating role of mental health as well as the differences among various student groups. Through a survey of 1236 students from 45 higher education institutions in China and the application of structural equation modeling for data analysis, this study reveals the mediating role that mental health plays between teacher competence and academic performance. The results of the study indicate that for low-grade (Year 1) and high-grade (Year 2, 3, 4) undergraduate students, their mental health status fully mediates the relationship between teacher competence and academic achievement. As grades increase, the correlation between college students' mental health and academic achievement gradually diminishes. For postgraduates, their mental health does not serve as a mediator between teacher competence and academic achievement. These findings are significant for educational institutions in formulating teaching strategies, as enhancing students' mental health levels can optimize educational outcomes and improve overall student well-being.