When the non-contact method is used to obtain the torsional vibration data of the shaft system, a faked torsional signal blended in the real torsional signal can decrease the measuring precision. In this paper, the characteristics of the faked torsional signal, induced by offset of fluted disc, is analyzed theoretically, and identified by using steady-state offset value of fluted disc. The synthetic processing method of signal was presented. Based on this method, the torsional vibration signal of a tracked vehicle powertrain was analyzed and corrected. The results shown that the provided method can promote the precision and accuracy of testing.