Aiming at the fatigue crack fracture problem of a speed-increasing gear of a wind turbine,based on the M-integral method,the change laws of the initial single-crack and double-crack growth gear crack expansion were explored.According to the analysis and calculation of fracture mechanics principle and finite element principle,the change laws of stress intensity factor and fatigue expansion cycle number were obtained.A gear crack model with only one crack was created,the stress intensity factor and fatigue growth life of the crack propagation were calculated;the second crack was created on the initial single crack model continuely,and the change laws of stress intensity factor and fatigue growth life of the first crack and single crack front edge were explored by changing the 〖JP2〗initial position of the second crack.The results show that as a whole,the stress intensity factor of the 〖JP3〗first crack in the double-〖JP〗crack is smaller than that of the single-crack at the beginning of propagation,and will be higher than that of the single-crack at the end of propagation,and there is an alternating process between them;when a double-crack occurs,one of the cracks will accelerate the propagation of the first crack in the double-crack and reduce the life cycle;the closer the distance between two cracks is,the faster the first crack accelerates.