Abstract: In order to solve the applicability of the existing specifications to the fatigue design of complex welded structures of deep-water floating platforms, the bottleneck of multi cylinder cooperative control technology under various complex loads has been overcome. The first international structure level fatigue test device with biaxial tension compression + biaxial bending composite loading and the full-scale fatigue test device for welded joints with tension compression + bending composite loading have been developed. A test method for fatigue properties of standard samples in air, seawater free corrosion, cathodic protection corrosion and other environments was established. A multi-scale, multi-environment and multi-load fatigue test platform of “material level - node level - structure level” welding structure was constructed. It can provide strong support for the fatigue design verification of my country’s development of ultra-deep water floating platform in the complex and harsh marine environment of the South China Sea.