By studying various work items of helicopter transmission key parts fatigue design
the methodology of fatigue design of key parts was discussed.And a fatigue assessing process of transmission system gear was advanced.By investigating the time between overhaul (TBO) and flight life on the outfield of transmission system
a fatigue evaluation technology which can be used to the whole life of helicopter transmission was proposed.Besides
basic contents and process of the fatigue evaluation were both listed.The methodology described in this paper can give some theoretical guidance and engineering practical significance on the helicopter transmission research