Based on the allocation methods for scarce resources such as water rights, sewage discharge rights and the establishment of allocation indexes, the theory of synergeticsis used to analyze the mechanism of drainage system, and the influence indexes are determined in accordance with the principles of equity, efficiency and sustainable development. The subjective weight determined by the order relation analysis method and the objective weight determined by the entropy weight method are combined and optimized through the set model of the game theory. Finally, the allocation model for water drainage right based on combined weight of game theory-TOPSIS model is established. Taking the allocation of drainage right of Sunan Canal as an example, the calculated results by the proposed model are compared with those by the order relation analysis- and entropy weight-TOPSIS models. The results show that the allocation model for water drainage right based on combined weight of game theory-TOPSIS model is feasible and reasonable, and the allocation of water drainage right is the result of the coordinated development of natural, social and economic systems. Among them, the rainfall, social water conservancy construction, historical disaster losses and so on have great influences on the allocation of water drainage right. The allocated results of water drainage right according to the size of the allocation quota are Changzhou, Wuxi, Suzhou and Zhenjiang.