A hollow twin-wheel caster structure of a luggage includes a wheel seat for coupling to the bottom of the luggage, the wheel seat having a horizontal inner annular hole; a hollow shaft unit inserted in the inner annular hole, two ends of the hollow shaft unit extending out of two sides of the inner annular hole to form a pair of coupling portions, the center of the hollow shaft unit being formed with a hollow portion communicating with the two ends of the hollow shaft unit; two plastic wheels fitted on the coupling portions; at least one bearing fitted on the hollow shaft unit; and a support member plugged into the hollow portion of the hollow shaft unit, the support member leaning against an inner wall of the hollow portion to prevent the hollow shaft unit from being compressed and deformed.