Abstract: The topside module structure of offshore floating production unit (FPU) contains a large amount of non-tubular joints, which are prone to fatigue damage during its service life. The structure of non-tubular joints is more complex comparing with tubular joints. Its fatigue assessment is complicated, and cannot be carried out by commercial offshore structure analysis software directly. In order to get the fast assessment of non-tubular joints fatigue life, in this paper, based on S-N curves approach combined with global structure analysis and local finite element analysis, a fatigue investigation on non-tubular joints was performed. A fatigue prediction method of FPU topside module non-tubular joints was then developed. Based on the design case of an FPU upper triethylene glycol (TEG) processing module, the fatigue life of non-tubular joints was evaluated with the proposed method, verifying its applicability. Results indicate that under consideration of safety factors, the minimum fatigue life of non-tubular joints in the TEG module is 20.11 years, meeting design specification requirements. The module has passed review by American Bureau of Shipping (ABS), completed land-based construction and delivery, and has been successfully deployed in the Madura Sea, Indonesia, which proved the reliability of the fatigue investigation method for non-tubular joints. The relevant research conclusions can provide reference for fatigue analysis of similar non-tubular joints.