Drought events are one of the main factors driving changes in grassland ecosystem productivity. This study aims to investigate the spatiotemporal characteristics of drought in Inner Mongolia's grasslands and its impact mechanisms on grassland productivity. The findings show that: (1) From 1992 to 2018, the overall trend in Inner Mongolia's Gross Primary Productivity (GPP) was declined (56.54 %), with a decline rate of 0.364 gC center dot m(-2)center dot a(-1). Among the three grassland types, only desert steppe GPP exhibited an increasing trend. The Standardized Precipitation Evapotranspiration Index (SPEI) exhibited an overall declining trend, covering 95.54 % of the area. (2) The positive correlation between GPP and SPEI in Inner Mongolia's grasslands was the strongest (88.78 %), with a significant positive correlation in 35.44 % of the area. (3) SPEI has a significant positive effect on grassland GPP, with an influence coefficient of 0.203, and it also had significant indirect effects through soil moisture (SM), Vapor Pressure Deficit (VPD), and Normalized Difference Vegetation Index (NDVI). Among different grassland types, the effect of SPEI on meadow and typical steppe GPP gradually weakened, while its influence on desert steppe GPP progressively strengthened. This study provides important theoretical support for the sustainable development of the region's grassland ecosystems.