Because of long-term separation from parents, left-behind children are inclined to cultivate strong loneliness and salient problem behavior. Perceived discrimination may be an important risk factor influencing the loneliness and problem behavior of left-behind children and adolescents. However, there are significant differences in the impact of perceived discrimination on individuals. The protective factors possessed by individuals can reduce the negative effect of perceived discrimination. Class is a critical living environment for left-behind children and adolescents. The teacher-student and classmate relationship in class are likely to be protective factors for left-behind children and adolescents to resist the negative effect of perceived discrimination. This research aims to investigate the moderating effect of teacher-student relationship and classmate relationship between perceived discrimination and loneliness and problem behavior of left-behind children and adolescents, so as to verify whether teacher-student relationship and classmate relationship are protective factors for left-behind children and adolescents to resist negative effect of perceived discrimination. This research suppose that perceived discrimination would significantly increase the sense of loneliness and problem behavior of left-behind children and adolescents; teacher-student relationship and classmate relationship would significantly reduce the sense of loneliness and problem behavior of left-behind children and adolescents; teacher-student relationship and classmate relationship would weaken the direct effect of perceived discrimination on loneliness and problem behavior; the relationship between variables is diverse in different left-behind categories. In order to achieve the above objectives, Perceived Discrimination Scale, Teacher-Student Relationship Subscale and Classmate Relationship Subscale of Class Environment Questionnaire, Loneliness Questionnaire and problem behavior Questionnaire were administered to 894 left-behind junior middle school students from rural areas in China. The key results are as follows: (1) perceived discrimination positively predicts the loneliness and problem behavior of left-behind junior high school students; teacher-student relationship and classmate relationship negatively predict the loneliness and problem behavior of left-behind junior high school students; (2) the interactions of perceived discrimination, teacher-student relationship and mother migrant significant predictors of loneliness, simple slope analysis indicates that teacher-student relationship can weaken the correlation between perceived discrimination and loneliness of junior high school students from mother migrant families; the interactions of perceived discrimination, classmate relationship and parents migrant significant predictors of loneliness, simple slope analysis shows that classmate relationship can reduce the correlation between perceived discrimination and loneliness of junior high school students from parents migrant families. (3) the interactions of perceived discrimination, teacher-student relationship and mother migrant significant predictors of problem behavior, the interactions of perceived discrimination, teacher-student relationship and parents migrant significant predictors of problem behavior, simple slope analysis reveals that better teacher-student relationship enhances the correlation between perceived discrimination and problem behavior of junior high school student from mother migrant families and parents migrant families; the interactions of perceived discrimination, classmate relationship and mother migrant significant predictors of problem behavior, the interactions of perceived discrimination, classmate relationship and parents migrant significant predictors of problem behavior, simple slope analysis suggests that better classmate relationship promotes the correlation between perceived discrimination and problem behavior of junior high school student from mother migrant families and parents migrant families. The research showed that perceived discrimination is a risk factor influencing the loneliness and problem behavior of left-behind children and adolescents. Supportive teacher-student relationship and classmate relationship directly reduce the loneliness of left-behind children and adolescents and weaken the correlation between perceived discrimination and loneliness. However, it is noteworthy that better teacher-student relationship and classmate relationship may increase the correlation between perceived discrimination and problem behavior of left-behind children and adolescents. implications and limitations are discussed.