Abstract: Soil aggregate structure and stability are key indicators for evaluating soil structure and erosion resistance, and also an important means for assessing the effectiveness of ecological restoration measures. However, existing research lacks studies on the mechanisms underlying changes in soil aggregate stability under long-term ecological restoration conditions. To identify the effects of Grain-for-Green project (GFGP) on the composition and stability of soil aggregates in the tillage layer of the calcareous purple soil region in the central Sichuan basin, China, four sample plots with different years of implementing GFGP, including cultivated land (CL), Land with 25 years of GFGP (GFGP25), Land with 25 years of GFGP (GFGP50), and forest land (FL), were selected in this study. The spatial distribution characteristics of soil aggregate composition in the 30 cm tillage layer in different lands were investigated using a layered profile survey method. The soil aggregate stability was characterized by indicators such as the percentage proportion of dry-sieved aggregates larger than 0.25 mm (DR_0.25), the percentage proportion of water-stable aggregates larger than 0.25 mm (WR_0.25), mean weight diameter (MWD), geometric mean diameter (GMD), percentage of aggregate disruption (PAD), water stable aggregates ratio (WSAR), soil erodibility factor (K) and Fractal Dimension (D). Moreover, partial least squares path model (PLS-PM) was used to explore the key drivers of the effects of GFGP on the soil aggregate stability. The results revealed that uniform distribution trends were observed in the tillage profiles for different grain sizes of mechanically and water stable aggregates in CL. Moreover, the profile distributions of soil aggregates in GFGP25, GFGP50 and FL were primarily different in the content of mechanically stable aggregates of >5 mm and water stable aggregates of >2 mm, which showed fluctuating increasing and decreasing trends along the vertical direction, respectively. Notably, the content of mechanically stable aggregates of >5 mm in each land reached a maximum at the mid-slope location, while the content of water stable aggregates of >2 mm was smaller. Soil aggregate stability within CL showed a relatively uniform distribution throughout the tillage layer (0–30 cm). In contrast, significantly higher soil aggregate stability was observed in the surface layer compared to subsurface layer in GFGP25, GFGP50 and FL. Furthermore, soil aggregate stability on slope displayed a relatively uniform distribution in GFGP25. However, soil aggregate stability was significantly lower at the mid-slope position compared to other locations in CL, GFGP50, and FL, which was primarily attributed to the erosion processes. Compared to cultivated land, GFGP significantly enhanced soil aggregate stability in the tillage layer significantly, with increases in WR_0.25, WSAR, MWD, and GMD ranging from 33.37% to 41.59%, 33.96 to 44.64%, 23.18 to 36.02%, and 49.02 to 83.77%, respectively. This improvement was primarily indirectly achieved through enhanced soil physicochemical properties and soil aggregate composition, with an indirect effect coefficient as high as 0.717. Soil organic matter and bulk density were identified as key driving factors. Overall, this study provided a systematic understanding of the benefits of GFGP in improving soil structure and quality, and a reference basis for the future implementation and planning of GFGP.