Under the background of ecological civilization construction, comprehensive consolidation and ecological restoration projects (CCERPs) have been widely implemented to enhance regional ecosystem services (ESs). However, the mechanisms by which CCERPs influence ESs across terrain gradients remain unclear. This study analyzed the variations of five ESs, as well as the area and spatial distribution of five types of CCERPs in Jiangxi Province during 2000-2010 and 2010-2023. Using the XGBoost-SHAP model, we explored the driving mechanisms and nonlinear effects of CCERPs on ESs variation across three terrain gradients (Rank1, Rank2, and Rank3). Results show that the total area of CCERPs increased by 18.54 x 108 m2 in 2010-2023 compared to the previous period. Grain for green project (GGP) and low-efficiency forest renovation project (LFRP) accounted for the largest areas in both periods, together exceeding 70 %. Significant spatial heterogeneity in ESs variation and CCERP distribution was observed across terrain gradients: ESs in Rank3 exhibited continuous improvement, while those in Rank1 showed high fluctuation. Over 80 % of construction land reclamation project (CLRP), dryland-to-paddy conversion project (DCP), and water restoration project (WRP) were concentrated in Rank1 and Rank2, while more than 70 % of GGP and LFRP were distributed in Rank2 and Rank3. CLRP significantly improved carbon storage (CS), habitat quality (HQ), and net primary productivity (NPP) in Rank1; DCP enhanced soil retention (SR) and water retention (WR) in Rank1 and Rank2; GGP and LFRP had positive effects on all ESs, with the most pronounced impact on CS and HQ in Rank2 and Rank3. CS and HQ in Rank1 and Rank2 were more sensitive to construction land expansion, while NPP, SR, and WR in Rank2 and Rank3 were more influenced by precipitation and temperature change. Declines in ESs caused by non-CCERPs factors offset the enhancement brought by CCERPs. Across different terrain gradients, each type of CCERP exhibited an optimal implementation range for enhancing dominant ESs. Within this range, increases in CCERP area effectively promoted ESs improvement. This study deepens the understanding of the relationship between CCERPs and ESs variation across terrain gradients and provides a scientific reference for the zoned implementation and precise management of future CCERPs.