Ecological products are nature elements that maintain ecological security, guarantee ecosystem service functions, and provide well living environments. National parks are the crucial areas for representative ecosystems, natural landscapes and heritages, and wildlife species, and also the main areas for ecological products supply in China which play an important role in providing high-quality ecological products. Gross Ecosystem Product (GEP) is the sum of the ecological products value and can reflect ecosystem status and protection effectiveness objectively. We took the first batch of national parks as the research objects and calculated the value of their ecological products. The conclusions were as follows. (1) The total GEP of the national parks was 1081.36 billion yuan, and the main ecosystem service functions were water retention (420.09 billion yuan) and climate regulation (336.69 billion yuan), both accounted for 70.0%; the GEP per unit area of the national park was 6.5 million yuan/km² which was 1.4 times higher than the national average (4.8 million yuan/km²). (2) Three-River-Source National Park had the highest GEP (454.77 billion yuan), and followed by Giant Panda and Hainan Tropical Rainforest National Park (278.14 billion yuan and 226.34 billion yuan); Hainan Tropical Rainforest National Park had the highest GEP per unit area (51.41 million yuan/km²), and followed by Wuyishan and Giant Panda National Park (48.16 million yuan/km² and 12.23 million yuan/km²). (3) From 2000 to 2015, the total GEP of national parks increased 1.0%, and the GEP per unit area was basically stable. The GEP of Three-River-Source and Hainan Tropical Rainforest National Park increased significantly (3.1% and 1.0%), while Giant Panda National Park decreased 2.0% which mainly related to the reduction of the area of forests, shrubs and other ecosystems caused by geological disasters. By accounting of GEP, this paper aimed to assess the protection effectiveness of national parks, explore the results application in their construction, and promote green development and "two mountains" transformations in the national parks. This paper still had some difficulties and deficiencies. Firstly, due to the difficulty of obtaining data, this paper did not calculate the value of material products and cultural services of national parks; secondly, due to the large geographical span of national parks, it was difficult to obtain localized parameters that were mainly from references, and their accuracy need to be improved. This paper could reflect the state and changes of the ecological environment in a certain period of time within the national park, and provided a scientific basis for the ecological protection and management of national parks.