Abstract: Existing P2P systems can NOT achieve both individual rationality and system efficiency for the lack of efficient BA (bandwidth allocation) and accounting proposal. In this paper E-currency and game theory are brought to P2P and the difficulty of BA in it is discussed. The utilities of all customers are used as a benchmark and two main novelties are brought forward: the first is that the VCG algorithm is brought in to P2P, and the second is that emphasis is put on how to choose bandwidth by clients. This kind of client-based bandwidth allocation proposal is much more suitable for P2P. The detailed BA & accounting algorithm is presented and its practical application is discussed.