Abstract: The BitTorrent peer-to-peer content distribution system adopts the Rate-based Tit-For-Tat（Rate-based TFT） choke algorithm and Optimistic Unchoke（OU） algorithm as a peer selection strategy：Each upload peer employs the Rate-based TFT algorithm to preferentially choose four requesting peers with the highest blocks uploading rates for itself and employs the OU algorithm to randomly choose another requesting peer as its download peers.However，the upload peer which uses the rate-based Tit-For-Tat choke algorithm only considers neighbor’s direct contribution that is the number of uploading blocks for itself.The strategy restriction not only has low resource utilization rate but also can’t effectively ensure fairness between download and upload.In order to solve the problems above，this paper proposes a global Contribution-based（Contribution-based TFT） peer selection strategy：Peer’s global contribution is calculated in a period of time from both direct contribution and indirect contribution（That is the number of uploading blocks for other peers）.In reality，more contribution is equal to higher priority to download blocks.Experimental results show that the contribution-based peer selection strategy can improve the resource utility ratio of upload slice and decrease the time consumption for completely downloading the whole file and ensure the fairness in BitTorrent.