To investigate psychological status of medical students and evaluate effectiveness of online psychological crisis intervention during the COVID-19 epidemic, a sudden public health emergency. Methods: A total of 826 medical students were recruited. The psychological status of these students was evaluated using the Generalized Anxiety Disorder-7 (GAD-7), the Patient Health Questionnaire-9 (PHQ-9), and the Patient Health Questionnaire-15 (PHQ-15). Online psychological crisis intervention was designed based on the results of the questionnaires. The effectiveness of the intervention was evaluated by performing a retest of these questionnaires two weeks after the intervention. Results: Among 826 valid questionnaires, symptoms of anxiety, depression, and somatization were observed in 8.4% (69/826), 17.7% (146/826), and 13.8% (114/826) of the students, respectively. Medical students aged 20～30 had higher scores for somatic symptoms than those aged 31～43 (t=4.532, P=0.033). In the subjective evaluation of online psychological crisis intervention, 92.1% (761/ 826) of the students found it helpful. There were significant differences in the scores of emotional and somatic symptoms (Z=－ 6.170, P<0.001), GAD-7 scores (Z=－ 3.260, P=0.001), and PHQ-15 scores (Z=－ 2.200, P= 0.028) before and after the intervention, while the scores of PHQ-9 showed no significant difference (Z=－1.710, P=0.087). Conclusion: During the COVID-19 pandemic, medical students suffered from anxiety, depression, and somatic symptoms. Timely online psychological crisis intervention is effective in alleviating anxiety and somatic symptoms in these students.