A voltage measuring method for a supplying-end module of an induction type power supply system includes generating a coil signal on a supplying-end coil of the supplying-end module; clamping the coil signal to generate a clamp coil signal; performing signal processing on the clamp coil signal to generate a first signal and a second signal, respectively; generating a cyclic signal, a frequency of which is equal to a frequency of the coil signal; comparing the first signal and the second signal via a comparator to obtain a first time and a second time when the first signal and the second signal have an equal voltage level during a cycle of the cyclic signal; calculating a middle time of the first time and the second time; and sampling the clamp coil signal or the coil signal to obtain a peak voltage of the coil signal according to the middle time.