Introduction  Continuous simulation of rainfall-runoff is very important in many hydrological studies, including the effect of climate change on river flow, flood forecasting, and water resource planning. This phenomenon requires the identification of its components and formative variables. One of the most important hydrological calculations for a basin is the determination of the relationship between rainfall and runoff. The amount of water conversion from rainfall to runoff volume depends on the climatic and the physical parameters of the basin. In the hydrological calculations of a basin, determining the relationship between rainfall and runoff is very important.  Accurate calculation of precipitation and runoff at the basin level depends on the identification of its components, form-providing variables, and the use of an appropriate dependent model. The HEC-HMS software is a simulation-based hydrologic modeling software (with parameter optimization capability) developed by the US Army Hydrological Engineering Center whose first edition was presented in 1967 (Hydrologic Engineering Center, 2000: 4). In addition, in order to increase the accuracy of the input information entering into the HEC-HMS software, the HEC-GeoHMS has created an add-on called HEC-GeoHMS. One of the most important applications of this software is calibrating and estimating hydrological parameters in catchment areas. Due to the importance and the extent of using this software, many studies have been done. Methodology The catchment area of ​​the city of Uremia is located in the western part of Lake Urmia. Its approximate area is 167.75 km2 and its geographical location is between 82 ° 44 'and 58 ° 44' eastern longitude and 32 ° 37 'to 48 ° 37' northern latitude. The height of the altimeter station is 1591 m and the maximum height of the basin (located on the border between Iran and Turkey) is 3574 m. Figure 1 shows the location of the Urmia Shahirchay basin in the watersheds of Iran and Lake Urmia. In this study, the HEC-HMS model was used to simulate surface runoff. In addition, the HEC-GEOHMS integration was used to map the basin model. For this purpose, the data of the temperature and the precipitation data of the synoptic station of Urmia and the daily flow rate of the river flow at the hydrometric station of the Bardesour (located at the outlet of the basin) were used. Result By obtaining the basin model by the HEC-GEOHMS add-on in ARCGIS software and creating climatological models, controlling and entering other necessary parameters of the model was implemented. In simulation of rainfall-runoff of Chacha basin by HEC-HMS model, in the period of 2004-2013, the best calibration and validation period was selected to minimize simulation error. The base course was divided into two calibration (2004-2010) and validation (2010-2013) periods. The calculation of this parameter is necessary for simulation in mountainous basins, which are mostly snowfall. In this study, the temperature index method, one of the complementary methods of day-to-day modeling of snow modeling, was used. One particular way is to consider the specific amount of snow melting for any temperature above freezing point. For this purpose, the catchment area was divided into altitudinal classes and the percentage of area of each sub-basin in each altitude region was introduced into the model. Discussion and Conclusion Based on the results of the simulation in the calibration and validation periods, as well as the evaluation criteria of the model, it was found that the HEC-HMS model had a high probability in rainfall-runoff simulation of Shahrchay basin. It should be noted that the use of the …