Abstract: The predicting precision of the crack extension life of wind turbine blade main beams is affected by wind speed, crack length and angle, and others directly. The main beam of the blade is as research object. The hot spots of the blade main beam are determined based on the measured wind speed data of a wind farm. Then, the crack extension life is investigated through the extended finite element method(XFEM), with variable loads and different crack characteristics. Meanwhile, The crack extension life model is developed by J-integral, and then a life prediction method is proposed by combine J-integral and Sobol sensitivity. As a result, the crack extension life is reduced by 45%/5° and 16%/5° under three types of wind conditions, 5 m/s, 11.4 m/s and 25 m/s with crack angles of 5°, 45° and 45°, 90°. Crack length and stress are the key point for the prediction of crack extension life, with total sensitivity of 0.617 and 0.372, respectively. The mean values of crack extension life for the length range 1 mm, 2 mm are 1228, 18717, and the length range 2 mm, 3 mm are 570, 4964. This investigation provides a scientific basis for the evaluation of crack propagation life with regional characteristics.