Abstract： Objective To investigate the mental health status of the midshipwomen involved in Mission Harmony-2010 and its influencing factors, and also to provide scientific basis for the maintenance of mental health and selection of female ship crew.Methods With midshipwomen, female medical personnel, male shipcrew as study subjects, and with cluster sampling and stratified random sampling as study methods, questionnaires were conducted 4 times by using symptom checklist (SCL-90) and routine interviews were also made during our study.Results During the prolonged seagoing deployment, the rate of detection for mental health problems among the midshipwomen was 21.8%. Scores of various factors during the mid stage of deployment were obviously higher than those of the normal people. However, in the later stage, scores of various factors were slightly lower than those of the normal people. Statistical significance was shown in the mental health status of the midshipwomen, when a comparison was made between pre-deployment,early stage of deployment and the mid and later stages of deployment(P<0.05). Scores of somatization, depression, phobia and other factors were significantly higher than those of the norms of Chinese military personnel (P<0.05). Scores of interpersonal sensitivity, anxiety and paranoia were lower than those of the norms of Chinese military personnel, but without statistical significance. During the mid and later stage of the prolonged seagoing deployment, the mental health status of midshipwomen was worse than that of the male ship crew and female medical personnel(P<0.05).Conclusions Prolonged seagoing deployment could significantly worsen the mental health status of midshipwomen. It was necessary to give in-time psychological intervention so as to ensure the mental health of midshipwomen.