Considering the impact and the vibration that add to its driving system when high-speed MU running in the complex conditions, the rotor mechanical strength problems of a traction motor in MU power transmission system are studied, in this paper. The motor operating parameters when MU operating under different states, such as the starting process, the increasing voltage constant power process, and the constant voltage constant power process, are taken as the constraint boundary conditions in different situations. Considering the asymmetry of axial constraint, the distributions of both the Von Mises stress and the contact stress in rotor under different working states are analyzed, and the strength situation of rotor is evaluated. Then, the fatigue strength of rotor in a long duration rated operating is studied, and the fatigue weak position in rotor is found. The obtained results could provide a theoretical basis for the safety operation of traction motor in high-speed MU.