Based on the complex terrain and large city characteristics, the geographic information of Beijing was cut into 6458 grids and corresponding channels. Focused on the urban hydrodynamic and hydrographic process, the Beijing Urban Waterlogging (BUW) numerical model was built to simulate the ponding depth. Driven by highresolution precipitation observation, BUW can simulate the spatial distribution of the 21 July 2012 urban ponding in Beijing well, and the variation and max depth under concave bridges are close to actual condition too. In the scene of 2yr Return Period (2RP), there are some isolated ponding points inside the 4Ring Road. The depth and range of ponding increase in 10RP and 50RP. Under 100RP, there is servere pondings within the whole 5Ring Road with most exceeding 50 cm in the south. Facing the rainfall at the 21 July 2012 level, urban drainage will not be improved obviously with 20% of pipe diameter (20%+PD) broadening. The ponding gets relieved distinctly between the Roads of 4Ring and 5Ring and slightly inside the 4Ring in 60%+PD experiment. When the pipe diameter is broadened continuously, there is only shallow ponding between the 2Ring and the 4Ring in 100%+PD experiment and no ponding insides the 6Ring in 140%+PD experiment.