To investigate the effects and mechanisms of Restrictive Group Sandplay Therapy (RGST) on prosocial behavior in junior school students. Twelve junior school students with low scores in Prosocial Tendencies Measure for Adolescent were divided into the intervention group (n=6) and the control group (n=6). The intervention group received 6 times of Restrictive Group Sandplay Therapy, while the control group did not. After intervention, the prosocial behavior score of the intervention group was significantly higher than that of the pre-test (t=-3.722, p<0.05), but there was no significant change in the control group. Members are able to engage in more prosocial behaviors and are more accepting of themselves and others. Restrictive Group Sandplay Therapy can effectively improve prosocial behavior in junior school students. The intervention mechanisms include group psychological counseling and Sandplay Therapy.