In order to study the mechanism and the effect of the sensorless detec tion method for torsional vibrations of mechanical systems, a simulation test be nch for shafting torsion vibration was set up, which was driven by an induction motor and was loaded by a DC generator. Through the rapid onoff of a computer c ontrolled load circuit, the shafting torsional vibration was generated. The faul t information was extracted from the current signals using Hilbert transform env elope spectrum, and the fault information and the traverse vibration signal meas ured by an eddy current sensor were compared. The experimental results show tha t the mechanical fault information of the motor drive equipment mainly formed of torsional vibration is coupled to stator current. As compared with the traverse vibration detection, the sensorless detection method is more applicable to faul t detection of torsional vibration of mechanical systems.