The invention relates to an online detection method for a torsion vibration signal of an automotive power transmission system, and belongs to the field of automobile noise and vibration control. In the method, torsion vibration test and analysis are performed on a power transmission system of a running front-engine rear-drive independent suspension type vehicle. A testing disc and a rotating speed sensor are arranged at the tested position of the power transmission system and are used for measuring rotating signals of the power transmission system, performing self-adaptive filtering on the signals, performing time-frequency analysis on the filtered signals, and calculating the torsion vibration frequency of the system. The method is used for performing torsion test and analysis on the acceleration running working conditions of an actual vehicle, particularly the running front-engine rear-drive independent suspension type vehicle without a torsion vibration test rack. The testing disc and the rotating speed sensor are arranged at the tested position of the power transmission system and are used for measuring the rotating signals of the power transmission system, calculating the instantaneous rotating speed through the peak value detection, filtering, and calculating the torsion vibration frequency of the system through the time-frequency analysis of the filtered signals.