Watersheds are a vast area with different conditions that simulation and studying the processes of runoff and sediment production in these area are critical for managing and maintaining resources. The Kozatopraghi watershed with an area of 766 km2 is located in the south and upstream of the Garesou basin, Ardebil province. Between the hydrological models, based on the capabilities of the SWAT model, this model was used to simulate the hydrological processes of the area in sub watershed scale. Also, for a more accurate examination the rainfall simulator was used in the hydrologic response units (HRUs), the obtained results were generalized to the sub watershed scale. The results of SWAT model were assessment with statistical parameters R2, NSE and RMSE. In the calibration and validation periods these coefficients for simulation runoff obtained 0.8-0.74, 0.71-0.69 and 0.32-0.33, respectively, and for simulation sediment yield obtained 0.75-0.66, 0.72-0.64 and 35.27-26.39, respectively. Assessment the obtained results of rainfall simulator showed that Loamy soils, located in 8 HRUs have high effect in sediment yield production. The maximum runoff and sediment yield by rainfall simulator and SWAT model were observed in sub watersheds 13 and 1, that indicating poor and inappropriate conditions in these subwatersheds. Comparing the study methods showed that the SWAT model have better performance than rainfall simulator for simulation runoff. Also, the estimated sediment yield by this model is lower than rainfall simulator that is close to observed values.