Over the past few decades due to population growth and urban development, urban runoff has increased and led to different problems such as inundation of urban pathways, dissemination of environmental pollutions and flood hazards. In order to urban runoff management, it is necessary to estimate runoff rate correctly. SWMM is one of the most widely used models in estimating urban runoff. The goal of this research is to evaluate the performance of SWMM model in simulating flow rate in an urban watershed in District 22 of Tehran. At first, model required parameters were calculated. For model evaluation and validation, in three events, runoff was measured in the watershed outlet and was compared with simulated runoff. The model validation results showed that the simulated flow rates had good adaptation with the observed ones. The validation results were used for estimating optimum values of model input parameters. The results of SWMM model evaluation confirm model accuracy with NS= 0.72 and RSR= 0.53 and indicate the model ability in simulating urban runoff. So, SWMM model can be used for urban runoff management plans and designing urban runoff drainage networks in this area.