The 3D finite element model of planet carrier of wind turbine speed- increase gearbox is built to calculate the stress- strain of planet carrier under unit static load. The fitting method of S- N curves of the planet carrier of wind turbine speed- increase gearbox parts is given based on the Germanischer Lloyd specifications（ GL2010）. The fatigue life analysis of the planet carrier of wind turbine speed- increase gearbox is carried out by using the rain flow circulation count method and Miner linear cumulative damage theory,and the fatigue life of the planet carrier is obtained. The structure is optimized based on the fatigue analysis. The reference for the fatigue life analysis of the planet carrier and designing of large power wind turbine speed- increase gearbox is provided.