Entrepreneurial behavior has been substantially addressed in entrepreneurship literature, but the mechanisms by which social capital influences entrepreneurial behavior among college students remain unclear, especially the potential mediating and moderating interplay among them. Therefore, drawing on social capital theory and the Stimulus-Organism-Response (S-O-R) model, this study proposed a moderated mediation model of social capital on entrepreneurial behavior. Sample data were collected via questionnaires from entrepreneurial team members participating in the Innovation and Entrepreneurship Competition in Southwest China. Results showed that (1) social capital has a positive impact on entrepreneurial behavior; (2) entrepreneurial passion partially mediates the relationship between social capital and entrepreneurial behavior; and (3) entrepreneurial risk perception positively moderates the relationship between entrepreneurial passion and behavior and thus enhances the mediating effect of entrepreneurial passion. This study provides insights into the internal mechanism of social capital on entrepreneurial behavior and also offers practical guidance for individuals, universities, and governments.