In order to reveal the influence of the environment on urban flood, the rainfall and flood are decomposed to four components. Then the multiscale model of urban flood is constructed in the Jialu River Basin in Zhengzhou city of China. The results show that the underlying surface is the main driver of urban flood. Moreover, rainfall and flood volume basically retain a linear relationship in the first three components, and the impact of underlying surface is mainly reflected in a3. The multiscale model has good simulation effect and prediction effect.