The invention provides a torsional resonance frequency measuring device and method applicable to a large-scale power generating equipment or a traction motor equipment with a rotating shaft, such as a large power grid-tied wind turbine. The invention is characterized by employing a machine-side converter existing in the grid-tied wind turbine to output direct currents to a three-phase PMSG (permanent magnet synchronous generator), such that a pulse torque is generated to mechanically excite a rotor of the three-phase PMSG. Afterwards, a control circuit of the machine-side converter acquires back electromotive force generated by the mechanically excited rotor so as to calculate the torsional resonance frequency of the overall drive-chain system according to the frequency spectrum of the back electromotive force.