Taking urban roof as the catchment area in Xinxiang City, the paper researched the hydrology and water quality process of each rainfall event so as to provide the basis for effective use of urban rainfall and control of non-point source pollution. The samples includes the contents of SS, COD and TN. The results show that the variation trend of pollutant index SS, COD in runoff is similar and tends to a steady value.the contents gradually decrease and reach a stable value with the duration of rainfall.With the accumulation of rainfall, the change amplitude of TN gradually reduce, but which has a rebound and increase tendency before the end of rain. The standard deviation rate of water quality indicator is in the order of SS>COD>TN. The first flush of roof runoff is clear, and the initial runoff amount is equivalent to former 1~3mm rainfall. The correlation between SS and COD, TN in runoff is good. It shows that the similar measures can be taken to remove them in controlling the runoff pollution. That the runoff pollutants flow into the receiving water body directly through urban drainage pipes has an important effect on its quality. The change of SS and COD is obvious.