Abstract: The assessment of disaster-causing hazards for the rainstorm event is a fundamental and key aspect of assessing the risk of rainstorm disasters, which can provide essential technical support for meteorological disaster prevention and mitigation. Using the hourly and daily precipitation data from 7 national meteorological observation stations and 120 regional automatic weather stations in Xiaogan City, as well as geographic information data, etc., a regional rainstorm event disaster-causing hazard that occurred in Xiaogan City on 12 August 2021 was evaluated base on dynamic assessment method of disaster hazard assessment of rainstorm process. By analyzing rainfall characteristic quantity, the disaster-causing factors were identified. Four disaster-causing factors were calculated using the information entropy-weight method, and the rainstorm event intensity index was calculated. The topographic-effected indices and the drainage-effected indices were determined as environmental factors based on analyzing the underlying surface characteristics in the rainstorm area. Then a synthetical index of disaster-prone environment was calculated using equal weighted summation of these indices. The disaster-causing hazard indices of the rainstorm event are composed of the weighted intensity indices of rainfall and the synthetical indices of disaster-prone environment. It was divided into five levels by using the Jenks natural breaks method, and the hazard level zonation chart for the rainstorm event was created using GIS. Finally, the hazard evaluation results were validated by the real rainstorm disaster data from the main affected area. The main results are as follows. (1) The "8.12" rainstorm event was characterized by its suddenness, heavy short-term rainfall, and concentrated precipitation, with 86.1% precipitation concentrated in 6 hours, and maximum precipitation in 6 hours of being up to a 50-year recurrence period, so the disaster-causing factors were selected by mainly considering the short-term precipitation. (2) The highest-level disaster hazard zones are located in most of Xiaonan district, central Yunmeng, north-east Yingcheng City, and southwest Anlu City, while the higher-level disaster hazard zone covers almost all the central part of Xiaogan City. Note that the results depend on the rainstorm intensity, the environment of the terrain, and the river network. (3) The highest- and higher-level hazard zones were areas corresponding to the regions with heavy rainstorm damage, with the actual disaster level reaching the "major" disaster level. The hazard assessment results actually reflected the actual losses in the main affected area.