A data determination method for a supplying-end module of an induction type power supply system includes generating a current signal on a resonant coil of the supplying-end module according to a modulated signal of a receiving-end module of the induction type power supply system fed back from a resonant coil of the receiving-end module to the resonant coil of the supplying-end module; amplifying the current signal to retrieve a plurality of peak values of the current signal; setting a reference voltage according to magnitudes of the plurality of peak values; comparing the plurality of peak values with the reference voltage to generate a comparison result; and analyzing the comparison result to obtain modulation data of the receiving-end module of the induction type power supply system.