Contexts like gestures, emotions, situations are very useful when a person interacts with other persons or nearby situation. On the contrary, computer can not use contexts efficiently. But computing-aware computing now is becoming more and more important since pervasive computing was put forward by Mark Weiser in 1991. The research of context-aware computing, especially its system infrastructure, is surveyed. The main contribution of this paper is an innovative system infrastructure conceptual model and the key problems of the model are discussed in detail.