Context-aware mobile computing belongs to the field of ubiquitous computing. It aims to enable device to provide better service for people through applying available context information. In this paper, context-aware mobile computing was elaborated. Firstly, the history of definition of context was summarized, and then the new classification of human-centric context was proposed. The acquiring and application of context information was generalized in the following part. On the basis, the issues in context-aware mobile computing were pointed out and finally the architecture of context-aware Q&A service was presented. Although the context-aware Q&A service can not solve all the issues introduced in this paper, it can be considered as an attempt to provide mobile service through mining of previously gathered context information sensed.