Abstract: This paper provides a method to determine whether a compressor or a turbine rotor is the major unbalance rotor according to the vibration signals measured from transducers mounted on the engine ease. The method only needs to choose two or three thansducers sensitive to unbalance responses in different places. The major unbalance rotor can thus be recognized by comparison of the vibration data measured at some sensitive speeds with the standard vibration data which have been previously measured and analyzed. The method can be readily applied to rotor balance of aeroengine in field and save time and cost.