Nowadays, there are too many models in the world for simulation of hydrological processes, such as the SWAT physically based model. The SWAT model is a continuous and physically based hydrologic model that is the smallest unit in this model is Hydrologic Response Unit, and all hydrological processes are simulated in each of these units. This model can simulate runoff, sedimentation, erosion and chemical transfer in complex basins, taking into account different information layers such as soil, land use and digital elevation model of the basin. The first step in using these models is to prove their ability to simulate the water cycle of the basin. The SWAT model in Barandozchay basin simulated the monthly time step flow and the parameters involved in the hydrological processes calibrated. The SUFI-2 algorithm used in order to the calibration of the model. The time period of 2000-2011 and 2012-2016 were used for calibration and validation, respectively. The results of the calibration of monthly discharge with P-factor, R-factor, and NS criteria were 0.71, 0.32, and 0.66 and in validation process were 0.63, 0.36, and 0.51 respectively in Ghasemlou station. The results revealed that the high ability of the model in river flow simulation. Due to the weakness of empirical models in estimating watershed processes, it is recommended to use the physically based models in simulation of these processes.