A rotor assembly includes a rotor body having two rotor ends, a rotating shaft penetrating the two rotor ends, and two rotor end plates. The two rotor end plates are pressed to fit correspondingly the two rotor ends, and each rotor end plate includes an inner ring structure and an outer ring structure. The inner ring structure, made of an iron-based material and used to sleeve the rotating shaft, has a first outer-ring peripheral surface and a first thickness. The outer ring structure, made of an aluminum-based material, includes a first radial segment and a second radial segment. The first radial segment, wrapping the first outer-ring peripheral surface, has a second outer-ring peripheral surface and a second thickness larger than the first thickness. The second radial segment, wrapping integrally the second outer-ring peripheral surface as a unique piece, has a third thickness larger than the second thickness.