Abstract: The grasslands of Inner Mongolia represent a typical region within the Eurasian steppe, dominated by temperate grassland vegetation. These ecosystems provide a wide array of ecosystem services, supporting both animal husbandry and local socioeconomic development, while also delivering essential ecological functions such as wind erosion control, soil and water conservation, hydrological regulation, and biodiversity maintenance. However, with rising global temperatures and increasing human activities, these vital ecosystems face growing pressures. The grassland has shown significant degradation, posing a serious threat to regional ecological security and sustainable development. Considering the environmental characteristics and ecological regulatory functions of grasslands in Inner Mongolia, this study proposes an ecological carrying capacity (ECC) assessment framework aimed at maintaining essential grassland ecological services. The method is further applied to quantify the spatial patterns of carrying status for grassland animal husbandry across Inner Mongolia. The grassland carrying capacity index was employed to compare the ability of grassland ecosystems to support animal husbandry across different league cities. The results suggest that the spatial distribution of annual average ANPP_W in grasslands of Inner Mongolia exhibited a gradual decreasing trend from the northeast to the southwest from 1991 to 2020. The Greater Khingan Mountains and Yinshan Mountain regions, characterized by significant topographic relief, high soil erodibility, and strong rainfall erosivity, showed the highest ANPP_W values, reaching 60 g/m²·a. The ANPP_F allocated for wind erosion control and sand fixation displayed a spatial pattern decreasing from west to east. In Hulun Buir, the southeastern Horqin Sandy Land, and the central Ulanqab Plateau, where terrain is relatively flat and surface deposits are abundant, ANPP_F values were higher, typically exceeding 80 g/m²·a. Overall, the range of ANPP_S required to sustain ecosystem service functions in Inner Mongolia varied between 30 and 240 g/m²·a, showing a spatially decreasing gradient from northeast to southwest. In most areas, the ANPP_S required to maintain natural regeneration of grassland ecosystems was relatively high. From 1991 to 2020, the ECC of the grassland ecosystem in Inner Mongolia was 78.65 million sheep units, while the actual total livestock was 104.36 million sheep units. The livestock demand of grassland resources exceeded the supply capacity. The ecological carrying pressure index of grasslands in the entire study area ranged from 0.62 to 8.68, and the economic carrying pressure index ranged from 0.21 to 2.79. The ANPP occupied by the natural renewal of grasslands was relatively large, thus greatly reducing the ECC of grasslands in Inner Mongolia. Spatially, the ECC of animal husbandry in the eastern grasslands of Inner Mongolia was relatively high, while the overloading situation of animal husbandry in the western grasslands was more serious. This study uses ANPP to characterize the provision of three ecosystem services; however, when considering functions such as biodiversity maintenance, water conservation, and atmospheric purification, ANPP may be insufficient to reflect the magnitude of these services. It is therefore necessary to incorporate additional functional indicators of ecosystems to improve the accounting framework for ECC based on ecosystem services. The research framework proposed in this paper provides a new direction for estimating grassland ECC. The findings can inform decision-making for sustainable grassland resource utilization and regional ecological management, thereby effectively supporting initiatives such as grassland ecological compensation, grazing withdrawal and grassland restoration.