[Objective] The impact of the project to convert farmland to forest and grassland on terrestrial ecosystem carbon storage in the loess hilly-gully region was quantitatively evaluated in order to provide a basis for regional ecological construction. [Methods] The GIS spatial analysis method and the InVEST model were used to study changes in land use and carbon storage in the loess hilly-gully region from 2000 to 2020. [Results] ① From 2000 to 2020, the conversion area of cultivated land to forest and grass land accounted for 20.75% and 86.56%, respectively, of the total conversion amount of cultivated land, and the coverage rate of forest and grassland increased by 1.76%. ② The conversion of farmland to forest significantly improved the carbon storage service in the loess hilly and gully region, and carbon storage increased from 8.22×10⁸ t in 2000 to 8.26×10⁸ t in 2020, and reached a peak of 8.35×10⁸ t in 2010. ③ The increase in net carbon storage of the study area was more than offset the carbon loss, and the contribution rate of carbon storage returning forest and grassland was the largest, which was 38.82% and 22.58%, respectively. [Conclusion] Implementing the project of returning farmland to forest and grassland has had a significant positive effect on the carbon storage of the regional ecosystem. Forest and grassland construction can enhance ecosystem carbon storage services. Future research should focus on the carbon sequestration contribution of ecological restoration projects, the scientific management of forest and grass vegetation, and improving regional ecosystem services.