Urbanization has led to development the impervious surfaces and subsequently changes in urban hydrology. The aim of this study is investigate the effect of land use change and urbanization on the changes of runoff peak discharge in Zanjan City Watershed, Iran. In order to, Landsat Thematic Mapper (TM) images and Aerial photos of 1956, 2000 and 2012 has been processed by using IDRISI Selva and Geographic Information System software and land use maps prepared in six land use class and the trend of land use changes and urbanization determined. To analysis the hydraulic and hydrology behavior of three periods of land use changes and urbanization on the changes of runoff peak discharge, Stormwater Management Model (SWMM) was used. After the SWMM model calibration based on observation rainfall-runoff events, the results of model calibration and verification, confirmed the accuracy of the model simulation. The results of land use change and urbanization trend of Zanjan City Watershed show that urban areas in 2012 compared to 2000 and 1956, respectively, has increase 22.59 and 923.88 percent and in 2000 compared to 1956 has been increased 543.06 percent. The results of SWMM model show that land use change and urban development has led to increase the runoff peak discharge, so that the average change in runoff peak discharge show that it increase in 2012 compared to 1956 and 2000, respectively, 96.85 and 475.52 percent and in 2000 compared to 1956, 194.288 percent increase in average of runoff peak discharge is observed.