The growing number of new urban migrants is a critical issue facing the transitional China. Whether these new migrants can adapt to the new city life and achieve their life goals is closely related to the economic development and social harmony of the overall Chinese society. Among all the factors that may influence the quality of life of urban migrants, the role of media is increasingly salient. This study focuses on the impact of social media on new urban migrants’ social integration and subjective well-being. Based on an online survey of urban migrants in Hangzhou, this study revealed that social media use can indeed contribute to urban migrants’ social integration, particularly their perceived social identity and weak social ties, but helps little with strong social support and real world social participation. In addition, while social media use does influence urban migrants’ subjective well-being, different types of use may have different effects. If urban migrants use social media for writing and self-expression, they will feel happier. In contrast, if they use social media for reading and social observation, they will feel less happy. Finally, urban migrants’ social integration, particularly their level of social identity, is significantly associated with their subjective well-being.