Life in Esfahan province is dependent on Zayandeh Rud. Therefore, sustaining the quality and quantity of Zayandeh Rud water is of much importance. The first step for adopting correct management decisions is to have continuous awareness of water quality and quantity, temporal changes, and spatial variations and, eventually, specification of main source of pollution. One of the models being used worldwide in such studies is SWAT. The first step in using this king of models is to prove their ability to simulate hydrologic cycle in a the watershed. The main goal of this study was to assess SWAT performance in Zayandeh Rud watershed in order to simulate river flow rate values. Model Calibration and validation were done using average daily flow in four stations named Ghal’e Shahrokh, Zayandeh Rud Dam, Pole Kole and Varzaneh. Observed and simulated values were compared by statistics including R2, NS and COE values to evaluate the model predictions against the observed values. The results of these values for flows at four stations for calibration process ranged between 60.2 to 80.1, 59.4 to 79.0 and 72.6 to 82.0, respectively. According to previous studies and the quality of the data used in this study, these values seem acceptable. The values for validation period were 60.4 to 72.0, 60.1 to 69.1 and 64.7 to 70.8, respectively. Among these four stations, measured and simulated flows at Pole Kole and Ghal’e Shahrokh matched well and weak, respectively. In general, the results showed that SWAT could be a proper tool for simulating the flow rate values of the river.