Abstract: With the rapid development of facility aquaculture mode, fish welfare in aquaculture facilities has gradually attracted attention. The size of aquaculture spaces directly affects fish movement, and high-density intensive aquaculture has become one of the prominent features of facility aquaculture. Both the spatial dimensions of culture environments and stocking densities have complex biological impacts on fish, which significantly affects the welfare demands of fish physiology, behavior, and growth. In aquaculture facilities design, the comprehensive approach that considers the impact of space on fish welfare can enhance overall aquaculture benefits. This paper explains the profound connotation and development status of fish welfare concept, reviewing the research progress on the effects of aquaculture facility spatial size and stocking density on fish welfare. Additionally, it addresses and recommends future research concerns on optimizing aquaculture facility space to improve fish welfare. This review provides a reference for the research and application of fish welfare and the development of facility fisheries.