OBJECTIVE: To understand the mental health status of subway employees, and to explore the relationship among their mental health, psychological capital and work engagement. METHODS: Using the typical sampling method, a total of 2 758 subway employees from a rail transit group Co., Ltd in a city were selected as the study subjects. The Symptom Check List 90, Psychological Capital Questionnaire, and Utrecht Work Engagement Scale were used to investigate the mental health, psychological capital and work engagement of the study subjects. RESULTS: The screening positive rate of mental disorder of the study subjects was 15.6%(431/2 758), and the median scores of mental health, psychological capital, and work engagement were 108, 109, and 62 points, respectively. The mental health scores of the study subjects were negatively correlated with their psychological capital and work engagement scores [Spearman correlation coefficient(r_S) were-0.55 and-0.57, respectively, P<0.01]. The psychological capital score was positively correlated with the work engagement score(r_S=0.70, P<0.01).Mental health played a partial mediating role in the influence of psychological capital on work engagement(mediating effect was 0.07, 95% correlation coefficient: 0.06-0.08, P<0.01). CONCLUSION: The mental health status of the subway employees is good. Psychological capital of subway employees can not only directly affect work engagement, but also indirectly affect work engagement by influencing mental health.