The mathematical model which can simulate inundation process in urban area due to heavy rainfall has been newly developed. The network model in which streets, rivers andchannels are treated as a channel network is used. The discharge hydrographs obtained by the runoff analysis in the surrounding mountainous area are imposed as the upstream boundary conditions. A simplified sewerage model is also incorporated. The model is applied to Kyoto city area. The computed results show a good agreement with the record of inundation depth distribution in 1935. The flood risk of the present Kyoto city is also discussed.