National-level marine ranching plays an important role in enhancing the marine ecological environment, fostering social and economic development, and bolstering human well-being. Quantitatively analyzing the level of coordinated development of its “ecological-economic-social” benefits and the factors influencing them is of great theoretical significance and practical value for refining the new round of development planning and guiding its construction and management. Therefore, on the basis of establishing a theoretical framework for the interaction of “ecological-economic-social” benefits, shellfish and algae were selected as research objects. We calculated the levels of ecological, economic, and social benefits, explored the interrelationships among the three using the coupled coordination model, and analyzed the influencing factors by using multivariate linear regression and geographically weighted regression. The results showed that: (1) In 2015 and 2021, the ecological and economic benefits of national-level marine ranching for shellfish and algae were better than the social benefits, in which the ecological and social benefits were stable, while the economic benefits were more variable; (2) The degree of coordination of the coupling between the three benefits in each province was mostly low, with most experiencing severe disorder; (3) The level of openness to the outside world and the standard of living of fishermen contributed positively to the coordination of benefit coupling between shellfish and algae. Conversely, the level of science and technology, innovation capacity, and the level of social development had a slightly negative impact. In conclusion, shellfish and algal aquaculture in China's national-level marine ranching significantly contributes to the ecological, economic, and social systems. However, the merits and demerits of natural, social, and economic factors must be comprehensively considered to promote the sustainable development of marine ranching. •Shellfish and algae, as the main species of China's marine organisms, provide a guarantee for the country's food security.•The assessment of shellfish and algae benefits reflects the sustainable development level of marine ranching.•The relationships of shellfish and algae benefits vary due to factors, leading to discrepancies between theory and practice.•Integrating domestic and international marine ranching developments offers insights for China's marine ranching construction.