Abstract: The aero-engine blade is often subjected with high centrifugal force, air dynamic force, thermal loading due to high temperature and temperature differences between surrounding, and vibration loading, and in addition it is also subjected with erosion by wind, sand and wet medium. All the above-mentioned factors shall cause the blade to develop fatigue cracks, which will threaten the safety of the engine. Therefore, during the service of the engine, the blade shall be under periodic maintenance and inspection for which the disassembling of the engine is needed and extra cost is required for this periodic inspection. The paper introduces an ultrasonic testing means for the non-destructive inspection of the cracks in deep blade root, providing an effective method for the in-situ testing of the engine blade.