To investigate the impact of the number of rainwater outlets on urban drainage capacity in a hydrodynamic model that couples urban surface runoff and underground pipe flow in both directions, a hydrodynamic model for bidirectional coupling of surface runoff and underground pipe flow was constructed. A block generalized model experiment was conducted to validate the hydrodynamic model, which was applied in a typical block in Glasgow, UK. The results show that the constructed hydrodynamic model has high accuracy, and the Nash efficiency coefficients of the simulation results at each measuring point are all greater than 0.89. The model can accurately simulate the processes of urban surface runoff and underground pipe flow. Increasing the number of rainwater outlets can effectively reduce the submergence depth and the maximum submergence range, with the most significant effect on areas with severe waterlogging. When the total number of rainwater outlets increased from 124 to 244, the submerged area in areas with severe waterlogging decreased by 55% to 81%. Increasing the number of rainwater outlets can also shorten the inundation duration. As the total number of rainwater outlets increases, the inundation duration of measuring points in the study area is shortened by 43% to 51%. When the rainwater outlets are evenly arranged, the drainage efficiency is positively correlated with the number of rainwater outlets, but the rate of improvement gradually decreases with the increase of the number of rainwater outlets. The response of flood processes in different regions to changes in the number of rainwater outlets varies, and when setting up rainwater outlets, special attention should be paid to locally flooded areas. Keywords: urban flooding; hydrodynamic model; rainwater outlet; inundation depth; drainage efficiency; Glasgow 〖FL