Abstract: Under the background of global warming, the spatiotemporal correlation between extreme drought and heatwave events has intensified over time. Their compounding effects not only amplified their individual impacts but also exacerbated pressures on water resources, agriculture, and ecological environments. Based on the fifth-generation reanalysis data from the European Centre for Medium-Range Weather Forecasts (ERA5), this study calculated the Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Temperature Index (STI) and employed the Frank Copula function to construct the Standardized Compound Dry and Hot Index (SCDHI). This approach systematically revealed the spatiotemporal evolution characteristics of compound hot-dry events in the Mongolian Plateau from 1982 to 2023. Additionally, the study integrated a random forest regression model to identify and quantify the key climatic factors that influenced compound hot-dry events in the region. The results indicated that over the past four decades, the intensity, frequency, and affected area of compound hot-dry events in the Mongolian Plateau exhibited a significant decreasing trend. Among the climatic variables, STI emerged as the most influential factor affecting compound hot-dry events, with a feature importance value of about 0.5. This was followed by SPEI, temperature, and potential evapotranspiration (PET), with feature importance values of 0.3, 0.1, and 0.1, respectively, while the impact of precipitation remained relatively weak. This study underscored the necessity of incorporating the long-term impacts of compound hot-dry events into the protection and management of the Mongolian Plateau’s grassland ecosystem. It emphasized the importance of developing adaptive management strategies based on scientific predictions and risk assessments to enhance the resilience and sustainability of the ecosystem.