Due to voluntary participation, and lack of incentives or restrictions, we cannot make sure every peer in P2P networks adopts and abides by the assumptions that all peers contribute their resources willingly, then emerge these serious problems such as free-riding, unfair allocation etc.. Therefore, in this paper we bring in the ideas of supervising game in Economics, propose an adaptive incentive approach (SGIM) to allocate resources fairly and boost peers do more contribution, as will construct its mathematical model and use the notions of Nash Equilibrium to analyze the strategic choices by different peers. The experiments' results indicate that our paper's main contributions are: (1) fairly allocate the bandwidth of service providers with the idea of distribution according to work; (2) the free-riding and fair sharing problems can be solved effectively to some extent; (3) the whole system can be evolve into a "good" and "balanced" states from the view of game theory.