In view of the increasing needs for urban flood prevention in coastal cities, a study was performed on the flood mitigation scheme based on the source tracking method. With subcatchments used as the analysis units, the complex water volume correlation between urban subcatchments was investigated through establishment of an urban flooding model for simulation of the urban rainfall-runoff process. With the Longkungou drainage system in Haikou City taken as an example, PCSWMM was used to establish the urban flooding model with the source tracking method, and the results show that sources of accumulated water in the inundation area were identified quantitatively and contribution ratios of different subcatchments to the accumulated water in the inundation area could be obtained by the model, which provided a basis for the selection of reasonable flood mitigation measures for different subcatchments. The implementation of the flood mitigation scheme formulated based on source tracking results can reduce the accumulated water amount by 36. 10% in the serious inundation area, achieving the desired effect of flood mitigation.