Abstract: In order to determine whether wind turbine blades should be decommissioned,a calculation method based on the CLD model is proposed to estimate their life extension span. Firstly,the load conditions of blades under operating conditions are analyzed. The fatigue life under bending moment is analyzed using the S-N curve,and then the bending moment life（M-N）curve is defined. The CLD model of life extension estimation is established according to the mapping relationship between M-N curve and CLD model. The CLD model based on life extension estimation calculates the accumulated fatigue damage of the blades to be decommissioned. The sustainable life extension time is estimated based on the accumulated fatigue damage. Finally,the life extension span of a certain type of blade is estimated by using this method.