Abstract: Clustering analysis and Gini coefficient are applied for the first time to analysis of reservoir optimal operation rules. The present results show that this method is feasible. This paper also presents a distance Gini coefficient that is more effective in reservoir operation analysis than traditional similarity index. Cascade hydropower stations in the middle Jinsha reach should be operated by the optimal operation rules that adjust along with the high and low inflow changes, and these rules are unique combinations of three basic elements, guaranteed capability, increasing flow, and no-surplus flow, in a certain way that varies with the high and low inflow condition every year.