Abstract: Based on the effort-reward imbalance model, the mediating effects of social support between effort-reward imbalance and positive psychological capital of college students were examined and the question whether the effects were different on urban and rural students was explored. The participants were 1 318 college students, who completed questionnaires, including the Effort-Reward Imbalance for University Students (ERIUS), the Perceived Social Support Scale (PSSS) and the Positive Psycap Questionnaire (PPQ). The results are as follows. First, the effort-reward ratio (ERR) was positively correlated with over-commitment and negatively correlated with social support and positive psychological capital; over-commitment was negatively correlated with social support and positively correlated with positive psychological capital; and social support was positively correlated with positive psychological capital. Second, social support partially mediated the relationship between ERR and positive psychological capital. Third, the relationship between over-commitment and positive psychological capital was suppressed by social support. Fourth, the relationship between ERR and social support was significantly moderated by whether co-llege students were from urban or rural areas. Compared with the rural students, the influence of ERR on social support is more obvious among urban students.