An urban rainstorm model based on PCSWMM for Haidian Island in Haikou City was developed. The model was verified by three measured rainfalls events and the corresponding tidal graph records in 20081013, 20101005, and 20111005. The simulated waterlogging submerged positions and depths are basically consistent with the actual investigation situation, which shows that the model has high precision and reliability. It respectively evaluated the present situation of drainage networks and the waterlogging risks in Haidian Island in Haikou City by using design rainstorms of return periods of 1, 2, 5, 10, 20, and 50 years with the corresponding tidal levels. The result shows that the present situation of 84. 8% of the drainage networks in Haidian Island in Haikou City is less than 1-year design return period. Meanwhile, the waterlogging risk assessment of design rainstorms with 5, 10, 20, 50-year return periods and three measured rainstorms with the corresponding tidal levels are analyzed.