A synchronous data transmitting method includes receiving, by a supplying-end module, a plurality of data impulses of power transmitting signal according to a first operating clock of a microprocessor in supplying-end module, for generating a plurality of data frames, wherein the plurality of data impulses is transmitted by receiving-end module according to a second operating clock of microprocessor in receiving-end module; calculating time periods between data impulses corresponding to start bits of the plurality of data frames, for acquiring a plurality of data frame periods; comparing the plurality of data frame periods with a data frame time period, for synchronizing the first operating clock and the second operating clock; and turning on a receiving function of the supplying-end module in a plurality of receiving periods and turning off the receiving function in a plurality of closed periods, wherein the plurality of receiving periods corresponds to the plurality of data impulses.