The power shunt behaviors between planetary wheels make the planetary mechanisms high energy transmission density.However,offset load will cause the power of planetary mechanism can not be distributed according to the ideal state,increase the meshing force between gears,and affect the service life and reliability of the whole system.Based on the structural characteristics of planetary reducer of a heavy helicopter,the finite element simulation model of large-scale planetary gear train was constructed to carry out quasi-static mechanical and kinematic analysis of planetary transmission system.The dangerous stress history of each gear was obtained,which could provide load input variables for reliability analysis models.The gear strength data obtained from the bending fatigue test were used as the strength input variables for the reliability analysis model.The concept of statistical minimum sample size was used to transform the life of gears and wheel teeth,the reliability analysis model of planetary gear system was established,and the mathematical mapping of fatigue reliability of planetary gear system was completed under different states.Under offset load state,the reliability of the planetary gear system is 92.32%,which proves that eccentric load can affect the fatigue reliability of the system and reduce the effective service life of the gears.