The number of smoker in China is still large while most of them are unlikely to quit smoking. Majority of studies indicated that social support from significant others of smokers is particularly important for smokers during the cessation. Many evidences have shown social support from family and friends significantly predicting quitting intention. However, some studies did not find significant relationship between social support and intention to quit smoking. Based on the theories of social impact and social identity, the present study supposed that social identity for family and friends who providing social support would moderate the effect of social support on intention to quit smoking. In addition, with regard to the mechanism of social support influence quitting intention, the Stress-Buffering Model emphasized social support would reduce the negative physiological influence of stressors which is one of the original causes of smoking. Actually, more other reasons for smoking should be considered. Lots of theories and empirical studies indicated that quitting intention was significantly predicted by perceived risk of smoking. Given this, the present study supposed perceived smoking risk played mediating role on the effect of social support on intention to quit smoking. Questionnaires were used to test hypotheses and a total of 340 current smokers (the mean of smoking years was11.73, ranged from 1 to 48) participated in present study. The questionnaires included the sub-scales of emotional support and instrumental support for quitting smoking from Partner Interaction Questionnaire, the sub-scale of perceived smoking risk from Decisional Balance Scale, Identification Questions, and Intention to Quit Smoking Questionnaire. The mediation and moderation analysis were conducted by using PROCESS macro for SPSS. The results indicated that: (1) Social support for quitting smoking from family and friends significantly and positively predicted quitting intention among smokers. (2) The relationship between social support and quitting intention was moderated by social identity to family and friends who providing social support. With the high level of social identity, social support would positively predict quitting intention; while with the low level of social identity, the relationship between social support and quitting intention was insignificant. (3) The relationship between social support and quitting intention was mediated by perceived smoking risk. Perceived smoking risk, which was positively and significantly predicted by social support from significant others, positively associated with intention to quit smoking. It was concluded that the relationship between social support and intention to quit was moderated by social identity and mediated by perceived smoking risk. These findings were suggest that the inconsistent findings about effect of social support on quitting intention in previous studies might be resulted from different levels of social identity to the providers of support. Only with high level of identity, the social support would increase intention to quit. Meanwhile, it is suggest that social support which increasing perception of smoking risk and then increasing intention to quit smoking, performed the cognitive function besides buffering stress in the process of quitting smoking. Further studies should use multiple methods and construct diverse models to examine the relationship between social support and quitting intention among smokers.