Deep-sea offshore wind resources are extremely abundant. Large offshore wind turbine is the future trend to utilize of deep-sea offshore wind resources. Because of excellent heaving, pitching and rolling performances, tension-leg platform ( TLP ) is one of best floating support structures for large wind turbine. However, under extreme environment condition, the large tendons which are required for large offshore wind turbine TLP platform will meet extreme response, even lead to damage. Extreme response of tendon of a 10 MW offshore wind turbine TLP platform ( an improved MOSES TLP ) in the extreme environment condition is studied here. It is showed that the global motions can meet the basic requirements for 10 MW floating wind turbine, where the maximum angle of TLP is less than 10⁰. Meanwhile, the maximum tendon tension of the TLP in the simulation is less than the breaking force, which meets the requirements of API rules on tendon of TLP.