Abstract: The research objectives are to reveal the eco-environmental quality of surface mining areas in semi-arid grasslands, separate the ecological cumulative effects of anthropogenic activities and examine their evolving trends. Based on the concept of ecological cumulative effects in mining areas, an assessment index called Surface Mining Areas Eco-environmental Evaluation Index (SMAEEI) and a quantitative evaluation model of ecological cumulative effects in mining areas suitable for semi-arid grasslands were developed. The Shengli Coalfield in Inner Mongolia was selected as the study site to analyze the spatiotemporal distribution patterns of regional eco-environmental quality and ecological cumulative effects from 1986 to 2020, and the differences between cumulative effects caused by major anthropogenic activities. The results show that: ① the SMAEEI is applicable to the surface mining areas in semi-arid grasslands and can objectively rank the eco-environmental quality across different land-cover types. The study area exhibited an extremely significant decline in eco-environmental quality over the past 35 years, with diminishing spatial differences. Open-pit mines, expanding urban areas, Xilin River wetlands, and northern grasslands experienced extremely significant or significant degradation trends. ② The quantitative evaluation model of ecological cumulative effects for the surface mining areas in semi-arid grasslands can exclude the influence of climate factors on ecosystems, effectively quantify the cumulative effects of human activities on mining area ecosystems, and reveal their direction, magnitude, and spatial extent. The Change of Ecosystem Service Value Cumulant (COESVC) in the study area decreased by a total of 11 861.570 3 million yuan, indicating a negative ecological cumulative effect and a decline in ecosystem services and functions. Areas with high and medium levels of negative accumulation were concentrated in degraded wetlands, grasslands, urban regions, and open-pit mines. ③ Surface mining and urban development exerted the most pronounced negative ecological cumulative effects per unit area. The former exhibited the most severe negative changes per unit time, and the latter had the greatest local impact and deviation in negative cumulative effects. Grazing resulted in negative ecological cumulative effects over a wider range and in larger quantities but with the least local impact. Compared with other human activities, the ecosystem services and functions were more stable in relation to grazing. The research outcomes facilitate the shift from the physical quantity changes of the ecological environment caused by human activities in mining areas to value-based descriptions, providing a feasible method for estimating the environmental damage costs of regional production and living behaviors in monetary terms.