In this paper, an experimental study determined the coupled bending vibration of an internal combustion engine′s bend axle and its impact on torsional vibration. The mechanism was elucidated by the expressions of output voltage and instantaneous speed under the influence of bending vibration, based on the voltage characteristics of the magneto-electric sensor. The laws and spectral characteristics of the pseudo torsional vibration caused by the bending vibration were studied. The amplitude of the pseudo torsional vibration signal increased with the bending vibration amplitude and the measurement error at different times, and the teeth increased at a different pace. The main components of the pseudo torsional vibration signals were the precedent and following order of the bending vibration, with the latter being larger than the former, which was consistent with the experimental results. To effectively eliminate the influence of bending vibration, an integrated experimental device was designed. The research provides a theoretical basis for improving the accuracy of torsional vibration measurements.