Perceived Social Support Scale, Career Adaptation Scale and Self-reporting Inventory were used by 1905 postgraduate freshmen to explore the mental health status of postgraduate freshmen and its impact mechanisms. The results showed that the detection rate of postgraduate freshmen's psychological problems was 25.7%, among which obsessive(21.2%), interpersonal sensitivity(11.4%), depression(7.7%) and anxiety(6.8%) were more prominent; Significant correlation existed among perceived social support, career adaptability and mental health(p<.01); Career adaptability played a mediating effect in the relationship between perceived social support and mental health in postgraduate freshmen(β=-0.21,p<0.001). Perceived social support affects the mental health of postgraduate freshmen by developing their positive psychological qualities. To improve postgraduate freshmen's mental health level, educators should enhance their perception of social support by strengthening humanistic care, on the other hand, they should enhance postgraduate freshmen's career adaptability by offering career courses, career activities and career counseling.