Depression and anxiety are common psychological issues among international medical students in universities, which have serious negative impacts on their learning and life. The present study aimed to evaluate the efficacy of positive emotional writing in alleviating symptoms of anxiety and depression, as well as enhancing subjective well-being among this population. This study was conducted at an international college of a comprehensive university in central China. A total of ninety-two participants who met the inclusion criteria were recruited to participate in a single-blind randomized controlled trial, in which participants were not aware that there was an experimental group and a control group. Participants in control received daily psychological care weekly for 8 weeks (n = 46). Correspondingly, participants in experimental group received the positive emotional writing intervention on the basis of daily psychological care. Self-Rating Depression Scale (SDS), Self-Rating Anxiety Scale (SAS) and General Well-being Scale (GWB) were used to evaluate the effect of the intervention. Data from 89 students who completed the entire study (experimental group, n = 44; control group, n = 45) were analyzed. After the intervention, the scores of SDS and SAS in the experimental group significantly decreased, while the subjective well-being score significantly increased. Although the SAS score of the control group after intervention was significantly lower than before, the decrease in SDS and SAS scores, as well as the increase in GWB score, were significantly greater in the experimental group than in the control group. The findings suggest that positive emotional writing can effectively reduce the depression and anxiety of international medical students, and significantly enhance their subjective well-being, providing ideas for management to solve the psychological problems of international medical students. ChiCTR2400087815. Registered at Chinese Clinical Trial Registry.