An electrocardiography signal extraction method is performed on a processor of a computer system and includes receiving an electrocardiography signal, performing a time-frequency transformation on the received electrocardiography signal to generate a corresponding scalogram, selecting a predetermined R-pertinent scale, performing the time-frequency transformation at the selected predetermined R-pertinent scale to generate a R-pertinent summarized response, obtaining a R peak position, selecting a predetermined QRS-pertinent scale, performing the time-frequency transformation at the selected predetermined QRS-pertinent scale, obtaining a Q peak position and a S peak position of the electrocardiography signal by finding relative maximum negative responses before and behind the R peak position respectively, obtaining a QRSon position and a QRSoff position by finding relative minimum second derivatives of the responses before the Q peak position and behind the S peak position, respectively.