This study evaluated the feasibility of integrating the carbon storage of grasslands in Gangwon province into the InVEST carbon storage and sequestration model using large-scale digital land cover maps. Land cover maps from 1980, 1990, 2000, and 2010, obtained from the Environmental Geographic Information Service, were analyzed, with 28 maps examined for each year. Grassland carbon storage in Gangwon province was estimated through the InVEST software. The findings indicated that the grassland area showed an increase in 1990, followed by a declining trend, contrasting with the continuous reduction observed in actual managed grassland areas. Discrepancies between mapped and managed grassland areas were attributed to the classification criteria of the land cover maps, which included non-forage land uses such as golf courses, ski resorts, and green spaces, resulting in overestimations of grassland areas. To enhance accuracy, the adoption of land cover maps with refined grassland classification criteria is necessary. Accurate representation of grassland areas in land cover maps is critical for reliable estimation of grassland carbon storage using the InVEST software.