[Objective] To analyze the impacts of the "Grain-for-Green Project" on the ecosystem carbon stocks in Guizhou Province. [Methods] Taking Guizhou Province as an example, the spatial and temporal distribution pattern and carbon stock changes of the "Grain-for-Green Project" in Guizhou Province from 2000 to 2020 were investigated by using ArcGIS in combination with the InVEST model. [Results] (1) During the 20-year period, land use in Guizhou Province had changed significantly, and the comprehensive dynamic had shown a downward and then an upward trend, which was 0.32%, 0.11%, 0.09%, 0.35% in order. There was an interconversion among cropland, woodland and grassland, with built-up land and waters mainly derived from cropland. (2) The total area of the "Grain-for-Green Project" from 2000 to 2020 was 2 381 700 hm², of which the land use transformation was mainly dominated by the conversion of cropland to forest land, which accounted for 84.86% of the total area of the "Grain-for-Green Project", and mainly in Zunyi, Bijie and Qianxinan Prefecture, etc. (3) A total of 257.40×10⁶ t carbon stock was added to the "Grain-for-Green Project" area from 2000 to 2020, showing a trend of gradual growth. Cropland shifted to forest land sequestered the largest amount of carbon, amounting to 239.89×10⁶ t (93.2%), and the soil carbon pool was the main contributor, with a carbon stock of 178.15×10⁶ t (69.21%). [Conclusion] The implementation of the "Grain-for-Green Project" helps to increase the regional ecosystem carbon stock. The carbon sequestration capacity of conversion of cropland to forest land is the largest, and the carbon sequestration capacity of conversion of cropland to grassland is smaller. The implementation of the "Grain-for-Green Project" in the future can prioritize the conversion of cropland to forest land, in order to increase the regional carbon stock.