Abstract: In order to study the changes between rainfall and runoff in the urbanization process of Beijing, the SCS model was applied to simulate the process of rainfall and runoff with some observed data in the Wenyu river basin. In addition, the changes of rainfall and runoff relationship in different hydrological years were also simulated. The results show that it is feasible to predict runoff using the SCS model in Wenyu river basin. No matter what the antecedent moisture condition is, annual runoff with different frequency of precipitation has an increase tendency as time goes on. In the same antecedent moisture condition, the absolute increase of annual runoff is followed by: wet year> normal year>dry year, but the relative increasion is: dry year>normal year> wet year. Under the same condition of antecedent moisture and rainfall frequency, the higher the level of urbanization is, the greater the runoff is.