Compared with non-left-behind children, left-behind children in China have lower social adaptation and the underlying reasons deserve further study. This systematic review and meta-analysis included 29 studies published between 2006 and 2019. Protective factors of Left-behind children's social adaptation were resilience (r=0.574), self-efficacy (r=0.538), emotional intelligence (r=0.421), self-esteem (r=0.404), positive coping (r=0.471), attachment (r=0.354) and social support (r=0.338) while risky factors were loneliness (r=-0.453) and social anxiety(r=-0.360). Age, birthplace, father/mother migration and the frequency of parent-child communication also have a certain impact on their social adaptation, but the effect size is relatively small. This study can provide some enlightenment for intervention programs and policy adjustment. More empirical studies focusing on influencing factors for social adaptation of left-behind children will be needed in the future.