As a special group derived from the urbanization process in China, rural left-behind children deserve great attention. Due to the absence of parents, whether left-behind children can effectively adapt to the social environment deserves great attention. Researchers have found that good social adaptation of left-behind children can buffer the negative effects of being left behind and enable individuals to creatively improve and develop themselves. Therefore, it is important to clearly identify the factors associated with social adaptation of left-behind children. Unfortunately, researchers pay more attention to single factors such as individuals, families or schools, or the joint factors of individuals and families, individuals and schools as causal factors for the social adaptation of left-behind children, and neglect to comprehensively discuss the impact on left-behind children's social adaptation from a multi-dimensional perspective. Among the influential factors, for left-behind children, self-consciousness in individual conditions is an important cognitive factor influencing social adaptation, school is the main social activity area for children, students form relatively stable teacher-student relationships and peer friendships during their interactions with teachers and peers, and school interpersonal relationships are sensitive predictors of different types of social adaptation for children. Parent-child communication in the family environment and social support in the social environment influence the social adaptation of left-behind children. Therefore, it is necessary for future research to consider the factors affecting the social adaptation of left-behind children from a multidimensional perspective of individuals, families, schools, and society. Based on Ecological systems theory, this study proposed a multilevel structural equation model to explore how self-consciousness, parent-child communication, friendship quality, teacher-student relationship and social support influenced the social adaptation of rural left-behind children, which can help them adjust themselves to adapt to the social environment and perform social functions. Data was collected from 2,520 primary and middle school students in 57 classes from 11 schools in Jiangsu Province, including 1440 left-behind children and 1080 non-left-behind children. They anonymously completed the Self-Awareness Scale, Parent-Child Communication Questionnaire, Friendship Quality Questionnaire, Teacher-Student Relationship Scale, Social Support Scale and Social Adaptation Questionnaire. Meanwhile, students’ demographic information including gender, grade, left-behind information were all obtained. All the measures had good reliability and validity. The initial model was established based on the results of the path analysis, and the structural equation model of the factors influencing the social adaptation of left-behind children was established through the comparison of competing models. The results revealed that: (1) Teacher-student relationships, friendship quality, and self-consciousness were positively and significantly related to social adaptation. Friendship quality indirectly affects social adaptation through teacher-student relationships and self-consciousness. (2) Parent-child communication indirectly affects social adaptation by influencing teacher-student relationships, friendship quality, and self-consciousness. (3) Social support indirectly affects social adaptation by influencing teacher-student relationships, friendship quality, and self-consciousness. Meanwhile, among the total effects of factors affecting the social adaptation of left-behind children, the effect values of friendship quality and self-consciousness were high. The study suggests that extra attention should be paid to the friendship quality and self-consciousness of left-behind children, while strengthening parent-child communication and improving the social support system, forming a joint effort of school, family and social education, and effectively improve the social adaptability of left-behind children in rural areas. This study enriches the Ecological systems theory，and have practical significance for improving the social adaptation of rural left-behind children and provides reference for educators.