Abstract: Ordos City is in the ecologically fragile area of agriculture and animal husbandry interlacing zone, which is the ecological barrier of the northern region of China and also an important coal energy production base of China, and belongs to the typical grassland type coal mining area with poor overall ecological resilience.At present,the coordination of coal field development and the environment has become an important issue in the construction of mining areas. The fragile ecosystem of grassland coal mining areas makes the environmental pollution caused by coal gangue more and more prominent. In order to clarify the physical and chemical characteristics of coal gangue and the ecological risks faced by grassland coal mining areas, through evaluating and studying the gangue physical, chemical characteristics and ecological risk, which were collected from a mining area in Ordos City. The results showed that the lithology of coal gangue is dominated by mudstone. The mineral composition is mainly quartz, kaolinite, dolomite and potash feldspar and the surface crack width is greater than 10 μm. The chemical composition is mainly SiO2, Al2O3 and Fe2O3, accounting for 53.17%—61.23%, 18.27%—22.55% and 1.92%—8.42% respectively. Elements such as Ba, Ga, Zn, Cu, Cr and V are highly enriched in coal gangue,and the mass fraction of trace elements in fresh coal gangue is higher than that in weathered coal gangue; the potential ecological risk of heavy metals Hg and Zn is at a serious pollution level, Cd, Cu and Pb are at a moderate pollution level, As and Cr are at a moderate level, Ni is at a light pollution level, among them, Hg is the pollution factor that contributes the most in the evaluation of the comprehensive potential ecological hazard index of heavy metals, resulting in the comprehensive index being at a very strong pollution level.The degree of heavy metal pollution is in the order of Zn>Hg>Cd>As>Pb>Cu>Cr>Ni,the probability of adverse biotoxic effects in the study area ranged from 33% to 81%.