This study aimed to explore the relationships among socioeconomic status (SES), social relations, and children's mental health. A sample of 19,487 school‐aged children was collected from the 2013–2014 wave of the China Education Panel Survey. Structural equation modeling was conducted with Amos (version 21) to test our theoretical model. Results showed that SES was not significantly related to children's mental health, whereas parent–child relations, peer relations, and teacher–student relations elicited complete mediating effects on the relationship between SES and children's mental health. On the basis of these findings, relevant theoretical and practical implications were proposed.