Abstarct: The erosion and sedimentation phenomena have many destructive effects on the environment and human life. One of the most important effects of the reservoir sedimentation is the reduction of the storage of reservoirs. The construction of the dam is one of the most popular methods for exploitation of surface water resources, which is a huge expense in the form of huge national plans. Reservoir sedimentation not only reduces the capacity and life of the reservoir, but also causes numerous problems in opening and closing the deep and semi-deep gates of the dam, increasing the reservoir surface and increasing the evaporation and water losses. Shirin-Dare dam is located in the northeast of Bojnourd city, 65 km from the city, which is a dam with clay core and its initial volume at the maximum level of water level is 91.5 million cubic meters. Mathematical models are one of the important tools for predicting the amount of sedimentation in reservoirs of storage dams and estimating their useful life. The use of two-dimensional and three-dimensional models to simulate the hydraulic flow and sediment requires more complete information that most of these data are not available. Using the HEC-RAS4.1 numerical model, the sedimentation process of the Shirin-Dare dam was studied. After calibration of the model with using the hydrographic data in 2013 and 1396 of the reservoir of Shirin-Dare Dam, was implemented for different time periods and the sedimentation of the reservoir of the dam resulted from the implementation of the model in the longitudinal profile and a number of cross sections. The simulation results for 100 years showed that after this period, about %80 of the volume of the reservoir is filled with sediment, which means an average of annually %0.8 is reduced from the volume of the reservoir.