Solid waste management is a major challenge in urban areas throughout the world, especially in the rapidly growing cities of developing countries. As the largest developing country, rapid economic development, rising urbanized population and changed life style have substantially accelerated the volume of municipal solid waste in China. Recently, the concept of social capital has been successfully incorporated in the discussion on the interactions between society, economy and environment. It has gradually been a focal point of environmental management, which involves facilitating collective action via the cultivation of social capital. This paper extends the previous research by investigating the influence mechanism of social capital on the behavior of household waste separation through correlation analysis and econometric analysis. Household waste separation is a critical component of a successful integrated waste management, which has been playing an important role in waste reduction, resource utilization and hazardous waste disposal in developed countries. As accomplishing an effective solid waste management system has become a priority for the governments of all cities in China in the years to come, source separation of solid waste has been promoted as the key measure in waste management. Based on the household survey data, the empirical result shows that social capital exerts a significantly positive impact on the behavior of household waste separation. Tight social networks can reduce the opportunism and free-riding behavior of residents; the reward and punishment mechanism of social norms can effectively improve the predictability of other residents’ behavior, enhancing the confidence of residents in collective action of environmental protection; the self-reinforcement and accumulation of social trust has the strongest effect on the promotion of the behavior of the household waste separation. Meanwhile, householders’ age, education level, and party membership significantly activate the behavior of household waste separation. To resolve the issue of cities being besieged by solid waste, special attention should be given to the role of social capital in facilitating households’ collective action for solid waste management. However, it is worth noting that social capital in one community cannot be fostered automatically, and it is necessary to expand social networks of residents, to promote the trust among residents, and to cultivate the social norms. In addition, it is important to enhance the publicity of the knowledge of household waste separation and the exemplary role of communist party members.