The Loess Plateau is a key region for the implementation of the Grain for Green project. However, due to the combined effects of climate warming and the Grain for Green project, the quantification of the specific contribution of the project to ecosystem carbon sequestration remains challenging. Therefore, the MOD17 model and Random Forest model were utilized to simulate actual and climate-driven vegetation net primary productivity (NPP) and soil organic carbon (SOC). Then, the project's contribution to ecosystem carbon sequestration was quantified through actual and climate-driven vegetation NPP and SOC. The results indicated that: (1) the Grain for Green project was responsible for 60.05% of vegetation carbon sequestration, with spatial variations across subregions; (2) Without incorporating the CO2 fertilization effect, vegetation and soil carbon sequestration under the project increased by 4.29 Tg y-1 and 20.45 Tg, respectively; (3) The Grain for Green project accumulated significantly more SOC in the topsoil (0.14 kg m-2, 0-20 cm) than in the subsoil (0.08 kg m-2, 20-40 cm). Overall, the Grain for Green project has served as a crucial driver of ecosystem carbon sequestration, making substantial contributions to both the vegetation and soil carbon pools. Furthermore, these carbon sequestration effects exhibited distinct spatial heterogeneity and depth dependence, reflecting the differential ecological outcomes of the project across different geographic subregions. These findings provide a quantitative basis for guiding future afforestation and carbon management strategies on the Loess Plateau.