This paper presents the load spectrum and an engineering estimating method of the fatigue life of GRP blade of large-scale wind turbine. The distribution of aerodynamic loads which affect the fatigue life of the blade are analyzed using strip theory. The stiffening effects of the rotating blade are discussed, using the multi-body dynamics method. The influence of the dynamic stiffening effect on the blade vibration mode is then analyzed. The dynamic stress response caused by the deterministic dynamic loads such as aerodynamic load, gravitational load and rotating centrifugal load, etc., is calculated using finite element mode superposition method. The fatigue damage performance, fatigue damage rule and fatigue life estimate method of GRP blade are discussed. Based on the Palmgren Miner linear fatigue damage accumulation rule, a safety life estimate method is developed. The fatigue life estimate of the 1.5MW variable speed pitch regulated wind turbine blade shows that the GRP blade fatigue life estimate method is reliable and feasible.