To realize detection of rotor crack fault， taking one aero-engine as an example， we establish a simplified model for the low-pressure compressor part of the engine. Based on the principle that additional constant excitation will notably amplify the super-harmonic signal， we propose an interval control strategy for fault detection. Explicitly， we apply constant excitation in the velocity range where super-harmonic resonance takes place to amplify the resonance response amplitude， and skip excitations outside this velocity range to make sure that the main resonance is not affected. The simulation results in Simulink demonstrate that after applying interval control strategy， the super-harmonic signal is significantly amplified， and the super-harmonic resonance response peak amplitude at one-third and half critical speed is nearly 4.6 times amplified which makes it easier to identify in noise environment.