Dual-constraint spatial planning unlocks proactive blue carbon expansion across China's coastlines.

Coastal blue carbon ecosystems-mangroves, salt marshes, and seagrasses-provide vital climate mitigation benefits, placing them at the forefront of the global 30×30 conservation agenda. Maximizing these benefits across complex coastal transition zones requires spatial frameworks that reconcile intrinsic ecological suitability with human threats. However, existing conservation assessments in intertidal habitats remain largely reactive, fragmented, and blind to cumulative land-sea stressors and future expansion potential. Here we show that a dual-constraint spatial planning framework coupling habitat suitability with land-sea anthropogenic pressures across China's 18,000-km coastline unlocks a proactive blue carbon expansion capacity 7 to 24 times larger than current extents. Integrating 60 environmental variables and 13 anthropogenic pressure indicators reveals distinct latitudinal shifts driven by temperature-salinity dynamics alongside sharp land-sea pressure gradients in industrial bays. Systematic spatial optimization demonstrates that existing nature reserves cover only approximately 20% of high-priority zones, leaving over 70% of target areas dependent on active restoration rather than passive preservation. Our typology-based grid-governance framework bridges science and policy, providing a scalable model for coastal nations to execute proactive blue carbon management across threatened intertidal environments.