Understanding social support scale， career adaptation scale and self?evaluating inventory were used by 1 905 freshman of graduate students to explore their mental health status and its influence mechanisms. The results showed that the screening rate of the freshman of graduate students’ psychological problems was 25.7%， among which obsessive（21.2%）， interpersonal sensitivity（11.4%）， depression（7.7%） and anxiety（6.8%） were more prominent； there was significant correlation between the two among understanding social support， career adaptability and mental health（P<0.01）； career adaptability played a mediating role in the relationship between understanding social support and mental health in the freshman of graduate students（β=-0.21，P<0.001）. Understanding social support affects the mental health of the freshman of graduate students by developing their positive psychological qualities. To improve freshman of graduate students’ mental health level， educators should enhance their awareness of available social support by strengthening humanistic care， on the other hand， they should enhance their career adaptability by offering career courses， career activities and career counseling.