Policy interventions redirect land use/land cover (LULC) trajectories and consequently alter both individual ecosystem services (ESs) and the relationships among them. Resolving these effects is particularly important in major grain-producing regions, where agricultural production, urban development, and ecological conservation compete for limited land. Taking the Jianghan Plain in China as a case study, we developed a policy-LULC-ES analytical framework to quantify relative and cumulative effects during 2000–2010 and 2010–2020. The socio-economic interventions comprised dry-land -to-paddy-land (DTP), the food security plan (FSP), and rapid urbanization (RU); the environmental interventions comprised the grain for green program for forest restoration (GFGP-F), the grain for green program for grassland restoration (GFGP-G), and the river-lake connectivity project (RLCP). Changes in ESs and pairwise synergies were evaluated at regional and county scales. The FSP was associated with the largest relative increase in food production (40.29%) but also the greatest reduction in habitat quality (−5.84%). The RLCP produced the strongest improvement in water conservation (34.11%) and the largest decrease in carbon storage (−9.28%). Across the full 2000–2020 period, the cumulative RU-related increases in food production and water conservation were 34.45% and 31.29%, respectively, both lower than the corresponding maximum cumulative responses associated with FSP and RLCP. Except for carbon storage, policy responses were generally stronger during 2010–2020. Socio-economic development policies reinforced synergies linking food production with other ESs but weakened the relationship between water conservation and habitat quality. Eco-environmental protection policies exhibited the reverse pattern by improving the water conservation-habitat quality synergy while weakening the synergies between food production and other services and shifting these relationships toward the trade-off end. County-level analysis further identified the FSP and RLCP as the principal policy levers for agricultural and ecological outcomes, respectively. Coordinating these interventions is therefore necessary to limit cross-service trade-offs and improve land-use governance. The findings clarify how policy-driven land-use dynamics generate spatially differentiated socio-ecological consequences and provide evidence for sustainable land management in major grain-producing regions.