Abstract: With the development of society and economy, urbanization level continues to increase, which has changed the characteristics of the underlying surface. The water cycle has been seriously affected, leading to a series of urban water problems such as waterlogging and water environment pollution. Low Impact Development（LID） can alleviate the amplification effect of rainfall and flood caused by urbanization, and a key issue in the design of LID measures is to explore the impact of underlying surface changes on flood processes. This paper compares urban rainwater flood models and selects the Win-TR55 model, which is a small watershed design flood model. The core of this model is the SCS-CN runoff curve model, which is characterized by simple calculation process, less required parameters, and comprehensive consideration of the relationship between changes in basin precipitation, underlying surface type, and runoff. Based on the above model, the underlying surface of the Jiulong Ecological Park in Wuhan is analyzed under current, traditional, and low impact development conditions. The design flood process is simulated under different return periods, and the hydrological effects of low impact development are evaluated based on changes in the flood volume, peak, and inundation range. The results show that（1） under the three development modes, the CN value is the highest under traditional development and the CN value is the lowest under low impact development conditions. This indicates that in the low impact development mode, the type of underlying surface has been changed, the storage capacity has been increased, and the corresponding CN value has decreased, resulting in a decrease in flow rate.（2） Under the low impact development conditions, the reduction rates of flood volume for once every year, once every five years, once every ten years, and once every fifty years can reach 96.74%, 81.58%, 73.46%, and 61.13%, and the reduction rates for flood peaks can reach 94.14%, 70.63%, 60.64%, and 45.42%.（3） The reduction rates for the design inundation range can reach 74.35%, 63.60%, 51.14%, and 6.83%. From the simulation results, it can be seen that as the rainfall intensity increases, the flood control effect of low impact development gradually weakens. The study also found that as the rainfall intensity increases, the control effect of low impact development on rainwater and flood gradually weakens. The research findings can provide a hydrological basis for the design of regional LID facilities.