Abstract: After in-plant testing for 20 h, the straightener blades of the compressor in a certain type of aero engine showed longitudinal cracks in the middle of blade body. Appearance inspection, microstructure and fracture morphology observation and hardness testing were conducted on the cracked blades. The blade vibration at the working speed of the aero engine was studied and the formation cause of cracks was discussed. The results show that the crack mode of the straightening blade was high-cycle fatigue cracking. The cracks formed by rotating bending resonance caused by rear rotor in the working speed range of the engine. By adoption of frequency modulation scheme of thickening the whole blade, adjusting the speed at which the rear rotor blade stirred up the rotating bending resonance to above the maximum engine working speed, the crack formation of the compressor straightener blade could be prevented.