A physiological signal measuring method and a physiological signal measuring device are provided. The physiological signal measuring method includes the following steps: A first inputting signal having a first frequency, a second inputting signal having a second frequency and a third inputting signal having a third frequency are respectively inputted to at least two electrode sheets attached on a skin. A first impedance value corresponding to the first inputting signal, a second impedance value corresponding to the second inputting signal and a third impedance value corresponding to the third inputting signal are respectively measured. An interference impedance between the electrode sheets and the skin is obtained according to the first frequency, the second frequency, the third frequency, the first impedance value, the second impedance value and the third impedance value. A measured physiological signal is corrected according to the interference impedance to obtain a corrected physiological signal.