Abstract: Coal production will inevitably affect the ecological environment. At present, the most common method of coal mine ecological monitoring is the calculation of vegetation coverage based on NDVI. In the process of vegetation monitoring for open-pit mines in the grassland, it was found that the calculation of vegetation coverage based on NDVI would cause serious errors. In order to study the reasons for the formation of the error zone and provide a suitable method for ecological monitoring of grassland mining areas, Sentinel-2 data was used to calculate the NDVI of the study area using the method of remote sensing band inversion. In addition, the method of empirical comparison was used to study the NDVI distribution characteristics of the Shengli and Pingshuo mining areas. The results show that NDVI can well reflect the surface vegetation coverage in areas with certain vegetation coverage, but there will be serious error areas in the areas covered by coal in the mining area. The error phenomenon will appear in both study areas, and the impact will be more serious in the Shengli mining area. The reason for this error phenomenon is due to the insufficiency of NDVI's normalization algorithm, which makes it impossible to distinguish between coal-covered areas and low-to-medium-covered grasslands with similar characteristics in spectral curves.