Based on observed data from 212 hydrological stations in the Yangtze River Basin, this paper analyzes the nonlinear relationships among peak discharge, precipitation, antecedent soil saturation, and drainage area. It verifies the powerlaw relationships between peak discharge and precipitation as well as antecedent soil saturation, and quantitatively analyzes the relationship between peak discharge and the ratio of relative antecedent soil saturation to relative rainfall intensity (SPR). Specifically, the relationships between the basin mean slope and the coefficients (both the constant and the independent variable coefficients) of the linear fitting equation relating SPR to peak discharge are investigated.The results show that with the increase of drainage area, the influence of precipitation on rainstorm-induced floods weakens, while that of antecedent soil saturation strengthens. With the increase of SPR, peak discharge first increases and then decreases. The basin mean slope is positively correlated with the constant coefficient but negatively correlated with the independent variable coefficient.