For optimal multireservoir system operation, a stochastic dynamic programming based on genetic algorithm(GASDP) was developed in this study. In the suggested model, multireservoir system operating rules were derived using a feed-forward genetic algorithm on formulation of potential rerlease allocation for each water user within the system to decompose a multireservoir system into a set of single reservoir subsystem. The case study of three reservoir system in parallel at Umsong-gun of Chung-buk Province illustrated the methodology. The performance of the GASDP model was compared with the single SDP model and Conventional method used for deriving the multireservoir operating rules from optimization results. The GASDP model provided better performance in increasing the expected total discounted income and reducing water spills of the system than the other methods, but also it could avoid being trapped at the local optimum and overcome the dimensionality curse in searching processes.