In this study, NSGA-II is applied to multireservoir system optimization, and the appropriate distribution index is suggested. Here, a four dimensional multireservoir system in the Han River basin was formulated. Two objective functions are used to achieve nondominated solutions. NSGA-II effectively determines these solutions without being subject to any user-defined penalty function as it is applied to a multireservoir system, conflicting two multi-objectives. Most research by MOGAs only reveals a trade-off in the objective function space present, and thus the decision-maker must re-analyze this trade-off relationship in order to obtain information on the decision variable. Contrastingly, this study suggests a method for identifying the best solutions among the nondominated ones by analyzing the relation between objective function values and decision variables. Our conclusions demonstrate that NSGA-II performs well in multireservoir system optimization having multi-objectives.