Using the community of Tianfuheyuan in Xi'an City, Shaanxi Province as an example, a water quality and quantity calculation model was constructed based on the principle of the Storm Water Management Model (SWMM). The model parameters were determined based on the measurements and relevant studies in similar areas in China and abroad. To analyze the synergistic relationship between the runoff control rate and non-point source pollution load reduction rate in the study area under different rainfall conditions, 45 rainfall events with nine return periods and five rainfall peak coefficients were designed. The results show that the runoff control rate was linearly related to the pollution load reduction rate under rainfall conditions with the same rainfall peak coefficient. The coefficients of synergy of the fitted function curves for the four pollutants COD, TN, TP, and TSS were above 0.989. The rain peak coefficient had little effect on the slope and intercept of the fitted function curve. There was a highly linear relationship between the runoff control rate and non-point source pollution load reduction rate at the residential community scale, and the pollution load reduction rate can be deduced from the runoff control rate.