Simulation of the quantity and quality of urban runoff is an important process in the management and control of urban runoff pollution. Based on sensitivity analysis and calibration of the Storm Water Management Model(SWMM) parameters, we simulated the quantity and quality of urban runoff to the Mintong catchment from Kunming city. The results showed that the most sensitive parameter in the quantity model is the percentage of imperviousness. In the quality model, the maximum buildup possible and the buildup rate constant are the most sensitive parameters. The sensitivities of the washoff coefficient and washoff exponent are influenced by the rainfall intensity. The quantity and quality of the simulated and measured runoffs showed good correlation. The calibration is was satisfactory. The simulation results showed that the annual pollutant loads of urban runoff for TN(total nitrogen), TP(total phorphrous), and COD(chemical oxygen demand) are were 75.6, 8.5 and 697.8 kg hm^-2 a^-1, respectively. The load of urban runoff pollution is an important factor in the diffuse pollution in the Dianchi basin.