<p>Land-sea coordination is a conceptual and strategic goal for integrated water management in coastal areas, proposing a valuable interpretation for land-sea interaction and land-sea water sustainability, particularly from the perspective of coastal water eco-environment. This study establishes an integrated framework, including the indicator system, driver decomposition, and correlation mining methods, to evaluate the land-sea coordination of the coastal eco-environment. The evaluation methodology defines land-sea coordination as an integrated system consisting of surface water environment, coastal seawater environment, and land-sea ecology, assessing the coordinated quality of the three subsystems and decomposing their interactive and contributing influences. A case study measures the spatiotemporal characteristics of the coastal water eco-environment in Chinese coastal cities from 2015 to 2023, finding a general improvement in the quality and synergy of land-sea coordination from a water environment perspective while identifying key areas for land-sea coordination in major estuaries and bay areas. Driver decomposition and synergy analysis for subsystems of the land-sea coordination reveal their interaction and contributing influence on the land-sea coordinated quality of coastal water eco-environment were significantly heterogeneous and complex. Land-sea coordination evaluation for the coastal water eco-environment provides a novel framework for comprehensively measuring the land-sea interaction and integration, which would be of referenceable and practical value for integrated land-sea system research and policymaking.</p>