Well-being is an important goal for both life and education. As indicated by previous study, Chinese undergraduates’ ratings for present well-being were lower than their ratings for future well-being. It is necessary to understand the influence factors as well as the underlying mechanism of well-being to transform this high expectation into reality. The positive effect of social support on well-being has been confirmed by many empirical studies. And the main effect model of social support proposed by Cohen and Wills in 1985 identified that social support has a lasting impact on well-being. The model further indicated that social support can facilitate well-being because it provides a sense of predictability and stability in one's life situation and a recognition of self-worth. By definition, self-efficacy means someone's own assessment of how well one can carry out actions and interventions that are necessary for dealing with future situations. It reflects one’s personal action control as well as recognition of one’s competence. Hence, it might be self-efficacy which plays a mediating role between social support and well-being. Friend and family are the most important sources of social support for Chinese youth. However, many young people may migrate to other places away from hometown in pursuit of higher education. Being away from family decreases the protective effect of family support, which comparatively speaking makes friend support even more important. Therefore, this study focused on the influence of friend support and hypothesized that self-efficacy could play a mediating role between friend support and well-being for Chinese undergraduates. In addition, social comparison orientation also has some influence on well-being. As indicated by many studies, there is an interactive effect between social comparison orientation and factors related to self-concept such as self-esteem and self-certainty on psychological states. And an interactive effect of perceived control and social comparison orientation on well-being was also found by previous study. Because self-efficacy can also reflect one’s self-concept and has a close relationship with perceived control, the interactive effect may also be found between social comparison orientation and self-efficacy. Therefore, this study further hypothesized that social comparison orientation could moderate the relationship between self-efficacy and well-being. To test the hypotheses, the present study constructed a model to examine the mediating role of self-efficacy in the relation between friend support and well-being as well as the moderating role of social comparison orientation in the second path of the mediating effect of self-efficacy. 776 undergraduates completed a battery of self-report questionnaires measuring their friend support, well-being, self-efficacy and social comparison orientation. All the measures indicated good reliability in the study. And the following results were found: (1) Friend support was positively correlated with self-efficacy and well-being; self-efficacy was also positively correlated with well-being; social comparison orientation was negatively correlated with well-being. (2) Friend support exerted both a direct effect and an indirect effect on well-being; the indirect effect was through the mediation of self-efficacy. (3) Social comparison orientation moderated the second path of the mediating effect of self-efficacy. For undergraduate students higher in social comparison orientation, their self-efficacy had a significant ascending trend as the increase of friend support (bsimple=.14, t=3.39, p<.001); for undergraduate students lower in social comparison orientation, the ascending trend of their self-efficacy was more obvious as the increase of friend support (bsimple=.35, t=7.19, p<.001). (4) The indirect effect of self-efficacy was moderated by social comparison orientation, and the indirect effect was stronger for student lower in social comparison orientation. The study highlighted the mediation effect of self-efficacy and the moderation effect of social comparison orientation in the link between friend support and well-being. It contributes to a better understanding of the effect as well as the paths and conditions of social support on well-being for undergraduates. And it also provided constructive suggestions to facilitate the well-being of undergraduates.