Water is most essential natural resource for life but in absence of rain fall drought occurs whereas excess rain fall causes floods and soil erosion. In Nepal accurate information of water availability is lacking. Therefore, accurate simulation of hydrological parameter is important for water resource management. The present study has been conducted in Bagmati River Basin for hydrological simulation of runoff, one of most important parameter of hydrology using SWAT model. Input data for model as soil map, land use land cover map and meteorological parameter were prepared with the help of Arc-Gis, ERDAS and Ms-Excel software. The model was calibrated using field-measured discharge data at gauged station for six years (1997 to 2002) and validation was performed for two years (2003 to 2004). The monthly simulated runoff of the calibration and validation periods were found to match with their measured discharge value of coefficient with correlation (R2) in both the cases 0.917 and 0.92 respectively. The model simulated daily runoff is corroborated by reasonably high Nash–Sutcliffe simulation coefficients of 91.54% and 77.31% respectively for calibration and validation periods. Similarly, average annual surface runoff in 1997 to 2002 and 2003 to 2004 was 831.2 mm and 922mm, i.e. 40 and 43% of precipitation respectively. Similarly, total water yield and evapotranspiration was 71% and 23% of precipitation in both time period. Such type of runoff model plays vital role for water resource management. So, this model can be further utilized as a potential tool for water resource management of spring fed River Basin in Nepal.