Aimed at the problem that the study of the whole life cycle cost of the floating offshore wind turbine is insufficient in China, a method is proposed to evaluate the whole life cycle cost segmentation of the floating offshore wind turbines. The whole life cycle is divided into 6 stages, which are pre-investigation stage, design stage, manufacturing stage, installation stage, operation and maintenance stage and dismantling stage. The cost of each stage is subdivided into different sub-costs and the multi-level cost composition of the whole life cycle is obtained to obtain the key variables that affect the whole life cycle cost. Taken a semi-submersible floating turbine as an example, the cost composition of each stage of the whole life cycle is analyzed to obtain the most important cost, and it is minimized to improve the economics of the floating offshore wind turbine. The research shows that controlling the manufacturing cost and installation cost is the key to reduce the whole life cycle cost of the floating offshore wind turbine.