Objective To explore the mental health characteristics of preschool left-behind children in rural areas in Shandong province,evaluate the intervention effect and provide evidence for improving left-behind children's mental health. Methods A total of 735 sutdents were selected from 10 kindergartens with layer-cluster random sampling and investigated by Strength and Difficulty Questionnaire (SDQ),which was used to know the psychological status of children.Subjects were divided into intervention group and control group according to areas.After one-year psychological intervention,the subjects were investigated with SDQ again. Results The scores of hyperactivity,behavior problem and total score of difficulty among the left-behind children were higher than those of not left-behind (P<0.05).After intervention,the prevalence of abnormal of the five factors declined.The score of the left-behind children who were supervised by their mother or their grandparents(on their father 's side )declined.There was no statistically significant difference before and after intervention among the left-behind children who was monitored by their grandparents(on their mother's side)(P>0.05). Conclusions Preschool left-behind children has poor mental health;Appropriate intervention can effectively improve the mental health status of preschool left-behind children;The children who were monitored by their mother had the best intervention effect.