Optimal selection of dam type is a complicated decision-making problem. It needs not only the experienced experts familiar with practical engineering, but also objective decision analysis technology. Comprehensively analyzing various factors affecting the rockfill dam type selection, a hierarchical structure model is established. Considering the defects of AHP method and Entropy method in confirming weight, the two methods are combined together to calculate integrated weight. Then this model is solved using TOPSIS method. Finally the optimum scheme of dam type is obtained. The practical application shows that this method is easy and the results are reliable. It can provide support for making decisions in optimal selection of rockfill dam type.