Abstract: When the on-line operation of a traction motor reaches its mileage stipulated in the maintenance rules, advanced maintenance should be carried out. In the process of high-grade overhaul and magnetic particle detection of rotor rotating shaft, it is found many times that magnetic traces appear in a certain part of the rotating shaft. It is of great significance to analyze and determine whether the magnetic trace is related display (fatigue crack) or non-related display, pseudo-display, etc, so as to determine whether the shaft is scrapped and provide an important basis for the on-line operation evaluation of the traction motor.