Academic achievement may influence teacher acceptance, peer acceptance and parent-child attachment, and then influence their loneliness. Many studies found that there was close relationship between social relationship and loneliness. However, there was few study focus on the relationship between academic achievement and loneliness. In this study, the mechanism of how academic achievement may affect children’ loneliness would be explored. To determine the specific effect of social relationship on the relationship between academic achievement and loneliness, five models were formulated. The first, second, third and fourth were single-mediator models. They explored the mediating roles of peer rejection, teacher acceptance, parent-child attachment, respectively, between academic achievement and loneliness. And the fifth model, as a multi-mediator model, simultaneously explored the mediating roles of teacher acceptance, peer rejection, parent-child attachment. Findings from this study are intended to provide empirical supports for the strategies that the prevention and intervention of children’ loneliness. Attachment Security Scale, Peer Nomination Questionnaires, and Children’ Loneliness Scale were used to investigate 438 children from elementary school from Grade 4 to Grade 6. Academic achievement was measured by the scores Chinese, Mathematics, and English. To examine the mediator effect of social relationship, the Structural Equation Modeling was used. The results indicate that, the relationships among academic achievement, teacher acceptance, peer acceptance, parent-child attachment and loneliness are significant; when only one mediator variable was examined，teacher acceptance, peer rejection and parent-child attachment were all important mediators respectively between academic achievement and loneliness．The relationship between academic achievement and loneliness could be fully mediated by teacher acceptance，while parent-child attachment or peer rejection could be a partial mediator between academic achievement and loneliness．When multiple mediator variables are examined simultaneously，teacher acceptance, peer rejection and parent-child attachment together could fully mediate the relationship between academic achievement and loneliness; sufficient indices of fitness are obtained for the mediation model． Based on the results of the model testing, the conclusions as follows: teacher acceptance, peer rejection, parent-child attachment have full mediator effect on the relationship between academic achievement and loneliness; there are indirect relations between academic achievement and loneliness; there are direct relation between academic achievement and social relationships; academic achievement could predict teacher acceptance, peer rejection and parent-child attachment directly; there are direct relation between social relationships and loneliness; teacher acceptance, peer rejection, parent-child attachment could together predict loneliness directly.