The method for determining damage. conversion of main shaft of aeroengine is introduced. In accordance with the linear accumulating fatigue damage theory and S-N curve

the standard damage cycles per flight hours

or damage conversion ratio Ap for flight can he obtained from the comparative residual life tests of the shafts with different service life. The main shaft fatigue life tests indicate that even the worst main shaft can resist the standard load cycle

or predicted safe standard cycle life. If it is divided by Ap

the service life (hours) of a main shaft can be determined. Further

the determination method of target service life is provided for general maneuver flight load conbined with spin flight load.