A method for identification aeroengine rotor-stator rub-impact fault is proposed in view of the concept of the flexible casing design for dualshaft aero-engine. Rub-impact is recognized through seeking the characteristic frequencies from dynamic strain before strain bridges should be installed in the inlet or intermediate casing. A simplified rotorcasing rubimpact dynamics model is established, and the dual-shaft engine rubbing characteristic frequencies are analyzed. Through seeking the characteristic frequencies several rubimpact faults are identified accurately in flight test at a certain aero-engine. Theoretical analysis and flight test show that the casing strain can sensitively pick up rub-impact vibration signals. When rub-impact fault occurs the combined frequencies of the highrotor and lowrotor rotational frequency mΩH±nΩL will appear in vibration spectrum, and the rub-impact fault can be judged from the combined frequencies. The combination frequencies mΩH±ΩL appeared in vibration spectrum are felt to locate a high-pressure rotor rubbing. Similarly, the combination frequencies ΩH±nΩL are felt to a locate low-pressure rotor rubbing.