Abstract: Aiming at the transmission failure problem caused by fracture of the fixed spline shaft tooth of the output shaft of the walking planetary reducer of 200 kN rail manipulator during use, the on-site investigation, structural analysis, load calculation, working principle and damage causes analysis of the fault are carried out in this paper; and the corresponding maintenance, improvement, quick replacement plan and damage causes are verified in practice. The results show that these measures have remarkable effect on the reliability and service life of the reducer.