Flood  has caused financial and vital damages in the  Hajighoshan watershed in recent decade.In this study, we investigated  the efficiency of flood control structures in decrease of flood hazard and their effects in the downstream flow regime.  First, a rainfall-runoff model has presented by using HEC-HMS model.The rainfall- runoff model was presented and optimized  by using 5  past flood events and then was validated with 4 another flood events.The dams were simulated by using Elevation-Area method  in the validated rainfall-runoff model. The results showed that The efficiency of flood control dams in decreasing of flood hazard dependents on their location, reservoir volume and  the surface of watershed or  sub-basin which it controlled its runoff.