To explore the relationship between subjective well-being, prosocial behavior and social support, and to provide reference for promoting prosocial behavior of college students. A total of 259 college students were investigated online with Index of Well-Being, Index of General Affect, Perceived Social Support Scale and Prosocial Tendencies Measure. The overall level of prosocial behavior is higher, subjective well-being and prosocial behavior are both significantly and positively related to social support. Subjective well-being has a positive and significant predictive effect on prosocial behavior. Subjective well-being has a positive and significant predictive effect on social support. The mediating effect analysis showed that social support plays a full mediating role in subjective well-being and prosocial behavior. Prosocial behavior of college students is related to both subjective well-being and social support, social support plays a full mediating role between subjective well-being and prosocial behavior.