Dam reservoirs are cosnidered as impronatnt hydraulic structures in water resources management and flood control. Therefore, reservoir operation and method of water release has sepcial importance. In this study, a new alorithm is used for reservoirs operation. This alorithm is a combination of  Harmony Algorithm and Particle Swarm Optimization (PSO) algorithm, and supports these two algorithms such that it solves the problem of lack of balance between exploration and exploitation. This hybrid method  improves the harmony method so that the trap probability in local optimum is decreased. Moreover, the hramony method hepls to correct the responses which don’t fall in feasible space of the solution in PSO method. The hybrid method was used for Mahabad and Karun 4 dam reservoirs, aiming at reducing the shortages and/or enhancing hydropower generation. Results showed that the hybird method has closer resposes to global optimum, as compared to the other two methods. In additon, simulated results of water release, storage, and genrated power in Mahabad and Karun 4 reservoirs match very well to nonlinear-programing results obtained by using Lingo software.