In view of the characteristics of multi-objective and uncertainty and complexity of the water resources allocation, the optimization of water resources allocation schemes can be regarded as a multi-objective grey relational decision-making procedure. This paper, integrating the grey relational decision-making method and the evidence theory, researches on the optimization method of allocation schemes and proposes the grey relational decision-making method based on the evidence theory, wherein the evidence theory is used to excavate the information contained in the decision targets and the weight of each decision target is obtained by the distance function. Then, the grey relational decisionmaking method is applied to calculate the grey relational degree between the weighted situation vectors of the decision targets and the optimal weighted ideal vector of the decision targets based on the grey relational analysis (GRA), and the optimal scheme (or schemes) with the highest grey relational degree from the alternatives is obtained. Finally, we take the optimization of water resources allocation schemes of Tianjin city in China for instance to demonstrate the practicability and effectiveness of this method.