Based on the motion equations of an unbalanced spherical rotor with contactless suspension,three methods of MUM (mass unbalance measurement) are put forward to measure the total massunbalance, radical mass unbalance and radical mass unbalance of the rotor. Total mass unbalance isobtained when the unbalanced rotor plays as a simple pendulum in static situation. The pendulant pe-riod and pendulant midpoint indicate magnitude and direction of total mass unbalance of the rotorrespectively Analysis of the motion equations by using the averaging method yields that the rotor willdo a special side oscillation when an auxiliary system maks the rotor spin about its pole axis which isorientating toward the local vertical. The radical mass unbalance can be obtained by building a properdisplacement sensor to sense the amplitude of the side oscillation. Necessary analysis of the motionequaions also shows that when the rotor spins at a small angular velocity and the rotary axis is per-pendicular to the vertical, the p Based on the motion equations of an unbalanced spherical rotor with contactless suspension, three methods of MUM (mass unbalance measurement) are put forward to measure the total massunbalance, radical mass unbalance and radical mass unbalance of the rotor. Total mass unbalance isobtained when the unbalanced rotor plays as a simple pendulum in static situation. The pendulant pe-riod and pendulant midpoint indicating magnitude and direction of total mass unbalance of the rotorrespectively Analysis of the motion equations by using the averaging method yields that the rotor willdo a special side oscillation when an auxiliary system maks the rotor spin about its pole axis which isorientating toward the local vertical. The radical mass unbalance can be obtained by building a proper displacement sensor to sense the amplitude of the side oscillation. Necessary analysis of the motionequations also when the rotor spins at a small angular velocity and the rotary axis is per-pendicular to t he vertical, the p