Abstract: The hilly regions, characterized by complex terrain, scattered settlements, and frequent flash floods, present significant challenges in implementing flood prevention and disaster mitigation measures. There is an urgent need to identify suitable models for conducting flood risk assessments to support flood prevention and emergency response efforts. By extracting topographical data and historical flood records from Changsha County and Rucheng County in Hunan Province, topographical data was processed by using GIS technology, and a two-dimensional flood inundation analysis model was established using HEC-RAS software. The model simulated inundation changes for flood recurrence periods of 20 a and 50 a within the study area and analyzed the maximum inundation extent, inundation water depth, and flow velocity. The results indicated that the trends in flow velocity changes in Changsha County and Rucheng County were consistent with topographical changes. The maximum flood water depths differed by 1.8 m and 1.2 m, respectively, and the maximum flood flow velocities differed by 1.11 m/s and 1.36 m/s, respectively. Based on flood water depth classifications, the analysis identified the severely flood-prone areas primarily distributed in the Laodao River, Liuyang River and other basins in the southern of Changsha County, as well as Zhejiang River basin in the central part and Oujiang River basin in the northeastern of Rucheng County. The HEC-RAS two-dimensional model is suitable for simulating flood inundation in hilly areas and can capture the propagation characteristics and spatio-temporal distribution features of floods under such terrain conditions.