The pandemic of COVID-19 has had significant impact on the condition of mental health and social support of medical students. But the mechanism of how medical students’ mental health was affected by social support during the pandemic was still unclear. Method: Kessler10 and Social support rating scale were employed to conduct the empirical research of mental health and social support of medical students from 3 medical schools. Result: The results indicated that students from Nursing discipline, Grade 4 and low-income families were of higher possibilities of developing a mental problem. And medical students’ mental health was statistically significantly correlated with social support under the pandemic. Conclusion: A mental health screening program among medical students and a mental health network were recommended to find out population mental health condition and imply targeted intervention strategies according to the risk level. And new social support systems should be explored to increase the level of social support among medical students.