A method for monitoring resistance welding is provided, which includes receiving an input of waveform data obtained by converting current or voltage applied to a transformer welding gun into a digital signal through a teaching group filter; comparing the input waveform data with acceptance waveform data of current or voltage that is accumulatively stored through a destructive test; determining acceptance of a quality of a corresponding welding product if the input waveform data and the acceptance waveform data are equal or similar to each other within a predetermined error range, and determining rejection of the quality of the corresponding welding product if the input waveform data and the acceptance waveform data are different from each other; and outputting an acceptance or rejection message depending on the result of the determination.