With the rapid development of information technology, especially sweeping progress in the Internet of things, cloud computing, social networks and social media, the era of big data is coming. As a data-intensive science, social computing is an emerging thing that leverages the capacity to collect and analyze data with an unprecedented breadth, depth and scale. It represents a new computing paradigm and an interdisciplinary research and application field. A broad comprehension of major topics involved in social computing is important for both scholars and practitioners. In this paper, we give a brief survey of the various research fields in social computing. We present key concepts and analyze state-of-the-art of the field. The article not only sheds insights on social computing, but also affords conduit for future research in the field. Social computing has two distinct trends: One is on the social science issues, such as computational social science, computational sociology, social network analysis, etc; The other is on the use of computational techniques, such as social use, hedonic use and generative use. Finally some new challenges ahead are summarized, including interdisciplinary cooperation and training, big data sharing for scientific data mashups, and privacy protect.