In order to accomplish the fundamental task of establishing moral integrity in cultivation, Peking University has constructed a “second head teacher” system. In essence, establishment of moral integrity in cultivation is aiming for shaping of college students' values and moral behavior. Based on the situation since the implementation of the second head teacher system in school of Public Health, Peking University, this study conducted semi-structured interviews with 7 students from January 2021 to January 2022. The interview outline is designed based on social learning theory. After coding the interview text data of more than 50000 words, we extracted five themes of the education mechanism of the second head teacher system, including the establishment of trust relationship, the strengthening of trust relationship, the role of example in the process of building virtue and cultivating people, the internalization process of the role of building virtue and cultivating people, and students' feelings about the second head teacher system. The results show that it is easier for students to build a sense of trust by actively approaching students, making students feel valued and having something in common between students and teachers. A good teacher-student relationship based on a solid trust relationship helps students to follow teachers' role modeling. The role modeling of teachers may further promote students to actively accept the values transmitted by the “second head teacher” and internalize them into their own goals, so as to continuously strengthen their positive behavior and have a positive and a long-term impact on students' development. To sum up, this study analyzes the internal mechanism of the “second head teacher” system in the process of building morality and cultivating people, confirms its educational effect and has a positive reference for other medical schools to further strengthen the work of building morality of medical students.