A differential voltage sensing method for achieving input impedance matching comprises the steps of: providing a first bio-potential signal to a first variable resistor for generating a first signal； providing a second bio-potential signal to a second variable resistor for generating a second signal； differentially amplifying first and second signals for generating a third signal； selecting an operation band of the third signal for generating first and second logic signals； and dynamically adjusting one of the impedances of the first and second variable resistors according to the first and second logic signals, wherein each of the first and second bio-potential signals has a common signal voltage level and a differential signal voltage level.
