Urban flooding has gradually become a major natural disaster in many cities with the development of the urbanization, but the current urban flooding models are mostly based on hydrodynamic methods, requiring a lot of input parameters, so they are inconvenient in popularization and application. In this paper, Shanghai Urban Flooding Assessment Model (SUM) was established aiming at the downtown inside the outer ring with the generalized method. Through inputting the hourly rainfall, hourly continuous simulation to urban flooding was achieved. On this basis, using the disaster situation data and ponding monitoring data, we assessed the simulation results. The results indicate that the SUM can simulate the urban flooding situation in the downtown of Shanghai better. The catchment area increases with the increase of precipitation amount. Analysis of disaster threshold shows that the rainfall causing water logging disaster in Puxi of Shanghai is generally lower than that in Pudong. The disaster rainfall is less relatively in the central part of the city including Huangpu District, Xuhui District, Hongkou District, Zhabei District and some streets in Baoshan District.