The invention discloses a semi-submersible marine ranch, which comprises a hollow communicating rigid pipe framework and a detachable net arranged inside the pipe framework, wherein the top of the pipe framework is connected with a semi-submersible tower with a cylindrical structure, and moreover, the inner space defined by the pipe framework communicates with the inner space of the semi-submersible tower; the detachable net is provided with a main net, the culture space of which approximates the inner space of the pipe framework; the top of the main net is provided with a smaller opening, and moreover, the opening is connected with a net neck; and the main net and the pipe framework are connected with each other by adopting detachable fasteners. The detachable net mounted inside the pipe framework has the characteristic of large culture space at the stage of culture, and moreover, the depth of the semi-submersible marine ranch in water is greater, so the fish-protecting effect on stormy waves is more outstanding. The top of the top net neck is open, so a certain recreational fishing space can be provided. During centralized harvesting, the whole detachable net can be lifted for centralized harvesting as long as the connecting parts between the detachable net and the pipe framework are dismounted. The semi-submersible marine ranch has the advantages of novel structure, high arrangement stability, large culture volume and convenient convenience in harvesting.