To solve the quantitative problem of urban runoff at large scale， a distributed watershed hydrological model named soil and water assessment tool （SWAT） was employed to quantitatively simulate the urban runoff and analyze the temporal-spatial changes in Shaoxing City. The SWAT model was established by putting the Shaoxing City in a suitable scale watershed based on DEM analysis. And then the SWAT model was calibrated and validated using monitoring data from hydrological stations based on the parameter sensitivity analysis. The results show that the calibrated SWAT model perform well on modeling the annual and monthly runoff in both calibration and validation periods with an average relative error （from -5.29% to 8.81%）， coefficient of determination （from 0.91 to 0.96） and coefficient of efficiency （from 0.90 to 0.94）. Meanwhile， monthly runoff data from 1992 to 2011 at sub -watershed scale were obtained using the calibrated model. Besides， temporal -spatial changes of urban runoff was quantitatively analyzed and the critical source areas （CSAs） was finally gained by means of geo-statistic method （GSM）， which will provide the scientific basis for water resources protection and utilization.