For an incomplete spherical superconducting rotor, which has a flat face at the top and a hole at the bottom, respectively, and with highly rotational speed, the mass imbalance is very necessary. However, because of the special structure, the air suspension of the rotor fails as soon as the flat or the hole contacts with the air hole of an air-suspending cavity. Then, the rotor cannot be suspended steadily by air suspension. A metal gasket is added at the bottom of the rotor hole to control the rotor. In addition, an air-suspending cavity with six air holes symmetrically on the side of the cavity instead of at the bottom is used to carry out the air suspension of the rotor steadily. In this paper, a new method of mass imbalance measurement for the superconducting rotor with air suspension is introduced including the theoretical analyses and the experiments.