Hydrological models are simplified representation of the real basin system, which helps to assess basin function in response to different inputs and better understanding of hydrological processes. The HEC-HMS model is one of the most important hydrological models for Flood estimating volumes and discharge in watersheds. In this research, the HEC-HMS hydrologic model was used to simulate the runoff flow in the Sarbaz river basin in Sistan and Baluchestan province. For this, basin and sub-basins models were prepared using the Digital Elevation Model (DEM) map and using Arc Hydro and HEC-geo HMS extensions. Next, through integration of land use maps and soil hydrologic groups in the Arc GIS, the curve number map for the studied basin was obtained. The results suggest that this basin has low permeability and high runoff volume. The results showed that there is a good consistency between observed and simulated hydrographs at the basin outlet and values of model efficiency index at the validation stage with Nash-Sutcliffe efficiency and were 0.90 and 16.37respectively which indicates the high efficiency of the model in estimating peak flow in basins and sub-basins. Also, according to the results, in this basin, as returns period increases, the runoff volume and basin discharge will be increased.