An audio-data transmission method for an electronic device is provided. The method includes determining whether or not a plurality of external data sounds and a plurality of external identification sounds are received. The external data sound and the external identification sound are respectively on a data frequency range and an identification frequency range that is different from the data frequency range. The external identification sound includes N sounds of predetermined frequencies wherein N is a positive integer larger than one. When not receiving the external data sound and the external identification sound simultaneously transmitted by at least one external electronic device, the electronic device transmits a plurality of data sounds and a plurality of identification sounds. The data sound and the identification sound are respectively within the data frequency range and the identification frequency range. The identification sound includes the sounds of predetermined frequencies.