Abstract: In the process of trial operation of an axial compressor, the man-made operational errors lead to air backward intrusion in axial compressor. In the inspection process, the magnetic particle inspection found that there were 12 moving blades with cracks on the fillet of dovetail in the 16th rotor and there were some other defects on the matching surface of dovetail and mortise, such as wear prints and burn marks. These defects on the dovetail were analyzed by microscopic morphology, spectrum analysis, metallographic observation and mechanical performance testing to search for the causes of these defects. The results indicate that the excessive vibratory stress in blades caused by air backward intrusion, combining with the substandard mechanical performance of blades, are greatly responsible for the stress concentration on the fillet of dovetail, whith is the main cause for cracks; and the wear prints and burn marks are the consequences of producing fretting wear on the matching surface of dovetail and mortise caused by blades high frequency vibration.