Relief amplitude is one of the important topographic factors in the development of slope geological hazards, but the influence of scale of extraction unit on extracting of relief amplitude is seldom considered in sensitivity assessment studies. Xishan geological block was taken as the research area in Taiyuan City, Shanxi Province, ASTER GDEM V2 and the slope geological hazard distribution information in the research area in 2012 were used as data source in this paper. Arc GIS was taken as the platform, and the mean change point method was adopted to analyze the relationship between the relief amplitude and the peak distribution of geological hazards, the average relief amplitude and the peak of relief amplitude with scales of 2×2, 3×3, 4×4, 5×5,…,25×25, total of 24 scales. The results show that the optimal extraction unit behaved differently on the peak distribution of slope geological hazards, the average relief amplitude, and the peak relief amplitude, which were 9×9 grid, 12×12 grid, and 12×12 grid, respectively. By taking into account the evolutions of regional geomorphology and hazard evolution factors, the 9×9 grid was selected as the optimal extraction unit for topographic relief amplitude in the sensitivity assessment of slope geological hazard in the studied area, with the optimal statistical area of 0.072 9 km2.