In the process of installation of floating fish cages offshore, it is usually necessary to leave enough catenary tension for the mooring chain while fish cages are in position. However, due to the influence of construction cost and other factors, most floating fish cages in China often use fixed length mooring system connected by mooring chain and eye plate, and are not equipped with tightening ratchet and other forms of mooring chain tightening device, which is more difficult to connect. To solve this problem, based on the connection construction of one floating fish cage offshore, a connection technology was proposed to ensure catenary tension of fish cage in position. Based on catenary analysis equation, the connection tensioning force under different tide levels was solved, and the influence of environmental load on the connection process of the fish cage mooring chain was simulated by using CFD method. The feasibility of the connection technology was verified in the actual construction. The results show that the environmental force has a great influence on the cage connection, and the influence of flow load is much greater than that of wind load and tide level. Theoretically, the peak value of the tensioning force under Beaufort scale for wind speed level IV can reach to 94.22t, which is of reference significance for the future connection installation of such floating fish cages offshore.