The DSI (Drought Severity Index) during vegetation growing season in Inner Mongolia from 2000 to 2019 is calculated using MODIS products, and the applicability of DSI in Inner Mongolia is analyzed based on typical drought events and drought indexes such as MCI (Meteorological drought Composite Index) and VCI (Vegetation Condition Index). The results show that the average correlation coefficients of DSI with MCI and VCI are 0.509 and 0.839, passing the significance test of 0.05 and 0.01, respectively, with high consistency. Compared with MCI, DSI has a higher spatial resolution and can reflect the difference in drought resistance of different vegetation types, as well as the enhancement of drought resistance ability after the improvement of regional vegetation. Compared with VCI, DSI is less affected by NDVI saturation in high vegetation coverage areas, and has higher sensitivity in drought relief periods. DSI is suitable for drought monitoring in Inner Mongolia, and can be used in drought monitoring researches and operations.