A method of utilizing an audio signal to transmit data for conducting electronic transactions includes in a user device, converting user identification data into a first audio signal and transmitting the first audio signal to a base device; in the base device, converting the first audio signal into the user identification data; in the base device, transmitting the user identification data and transaction content to a server device; and in the server device, obtaining authorization of a validation entity by utilizing the user identification data and the transaction content, for obtaining a transaction number and transmitting the transaction number to the base device.