The invention discloses a method for comparing the rigidity of a hollow shaft rotor and a solid shaft rotor for a large DC motor, which verifies whether a structure of the hollow shaft rotor is superior to a whole structure of the solid shaft rotor. The method comprises the following steps: setting relative same parameters of the hollow shaft rotor and the solid shaft rotor; respectively measuringstructure parameters of the hollow shaft rotor and the solid shaft rotor; calculating steps comprising respectively calculating the flexibility generated by the weight of an armature at the center point of the armature, the flexibility generated by the weight of a commutator and the flexibility generated by unilateral magnetic force on the hollow shaft rotor and the solid shaft rotor, and calculating the total flexibility at the center point of the armature on the hollow shaft rotor and the solid shaft rotor, the percentage of total flexibility occupying a main pole air gap and the critical rotate speed of the hollow shaft rotor and the critical rotational speed of the solid shaft rotor; and comparing step, comprising comparing the percentage of the total flexibility occupying the main pole air gap of the hollow shaft rotor and the percentage of total flexibility occupying the main pole air gap of the solid shaft rotor as well as comparing the critical rotate speed of the hollow shaftrotor and the critical rotational speed of the solid shaft rotor.