At present, the marine national park in China remains in the exploratory stage. Bohai and Yellow Sea ocean island ecological geographical area is one of the 39 natural eco-geographical areas in the spatial layout of Chinese national parks. Firstly, by examining this area’s core values and essential protection scope, this paper puts forward that Changdao, a typical marine island ecosystem in the north, is the priority protection area of the Bohai and Yellow Sea area. Secondly, we comprehensively evaluates the core values of Changdao National Park from three aspects: temperate island - shallow sea wetland - a typical representative of the marine ecosystem, crucial habitat and migration channel of rare species, unique and rare ocean, and island geological heritage landscape. According to the relevant requirements of the National Park Establishment Code, the demarcation of the assessment area of the Changdao National Park, the identification of priority protection areas, and the determination of the scope of the national park are conducted step by step. Finally, some problems of current research are discussed. In short, this study not only conducts practical exploration for establishing of marine national parks in China but also proposes a set of scientific and feasible technical methods and paths for demarcating the boundary of national parks.