Effective ecological governance and sustainable land management require a clear understanding of how ecosystem service (ES) supply and demand are coupled and spatially matched. Across northern China’s agro-pastoral ecotone, long-term ecosystem restoration and rapid socioeconomic development have reshaped ES relationships, intensifying supply–demand conflicts and spatial mismatches. Using Duolun County in Inner Mongolia as a case, we examined the dynamics of supply and demand for six ecosystem services (ESs)—carbon sequestration (CS), sand fixation (SF), soil retention (SR), water yield (WY), forage production (FP), and crop production (CP)—over the 2000–2020 period. Geographical Detector and Geographically Weighted Regression were used to identify the primary factors driving spatial variation in ES supply–demand matching. A composite zoning framework integrating supply–demand bundles and risk categories was further developed to support differentiated management. Four major findings emerged from the analysis: (1) ES supply exhibited divergent trends, with CP and CS increasing substantially, FP increasing on a per-unit-area basis but decreasing in total production, WY remaining relatively stable, and the estimated amounts of SR and SF decreasing as erosion pressure declined; (2) ES demand generally increased with population growth, livestock expansion, and socioeconomic development, resulting in persistent local potential forage supply–estimated demand gap and a widening gap between potential CS supply and estimated demand; (3) land-use structure, NDVI, and population density were the dominant factors of spatial heterogeneity in supply–demand matching; and (4) four ecological management zones were delineated, with tailored strategies developed to reconcile ecological conservation and human needs. The findings demonstrate that improvements in ES supply through ecological restoration do not necessarily lead to improved supply–demand matching. The proposed county-scale framework for ES assessment, zoning, and management provides a practical basis for territorial spatial planning and ecological governance in agro-pastoral ecotone regions.