Abstract: Protected area is an effective tool for the protection of coastal and marine biodiversity. This paper presents a comprehensive overview of China′s sea-related protected areas and assesses the conservation status of typical coastal and marine ecosystems and important species using spatial overlay analysis. Here are the findings: (1) A total of 363 sea-related protected areas, covering an extensive area of 105000 km², have been established. Notably, marine nature reserves constitute 44% of the total number and occupy 84% of the total area. (2) The conservation efforts for shallow water habitats close to the coast are relatively more robust than those for deeper waters farther offshore. Specifically, the average protection ratio for estuary ecoregions stands at 14.5%, and that for littoral seas is 10.9%, while shallow and abyssal seas receive significantly less protection. (3) Mangroves are of particular concern in China, with more than half of the mangrove biome covered by protected areas. Conversely, the protection of coral reefs, seagrass and kelp biomes is inadequate, with only 10% of coral reefs and 15%— 16% of seagrass and seaweed biome likely to be effectively protected. (4) The current sea-related protected areas are insufficiently sized to safeguard the core habitats of large marine animals. Even for species like Sousa chinensis, Neophocaena phocaenoides and Tachypleus tridentatus, which typically inhabit coastal areas and attract great public attention, the protection gap exceeds 80%. We suggest that local maritime jurisdictional barriers be dismantled to incorporate crucial marine areas located further offshore in the development of national parks, focus on special habitats with large protection gaps such as coral reefs, seagrass and seaweed biome, and expand the scale of protected areas targeting migratory species (e.g. Phoca largha, Chelonia mydas), especially in their core habitats.