Objective To explore the mental health situation of left -behind students.Methods 207 left-behind students and 210 non-left-behind students were selected from 5 schools in Shan'xi Province.SCL-90 scale questionnaire was used to inves-tigate the mental health of the left -behind students.Results The mental health level of non -left-behind students was better than the left-behind students.Besides, gender and age differences were distinct between the two groups.Conclusion Psychological measurement technology has great influence on left -behind students'mental health.We should make analysis from the prospective of family, school and themselves so as to improve their mental health.