The invention discloses a method and a device for acquiring subway power supply quality. The method comprises steps that the current waveform data of common connection points of a subway power supply system is acquired; morphological filtering of multiple harmonic waves of the current waveform data is carried out, and the de-noising waveform data is acquired; Fourier transform of the de-noising waveform data is carried out to acquire the amplitude data of the multiple harmonic waves; power supply quality parameters of the power supply system are acquired according to the amplitude data of the multiple harmonic waves. Through the method, a technical problem of relatively low precision of the power supply quality parameters of the subway power supply system is solved.