A method and device for playing MPEG Layer-3 (MP3) files stored in a mobile phone is disclosed, which enables users to stereophonically enjoy the MP3 music stored in the mobile phone with expending battery power economically or even expending no additional battery power. The device can connect the mobile phone to speakers to enable the MP3 files stored in the mobile phone to be played openly so that the user can enjoy music without wearing earphones. The device also provides an electrical charger for the mobile phone and the audio amplifier to play MP3 music files stored in the mobile phone with a sound quality comparing that of high-end audio equipment and an economical expense of battery power; the device can apply to all the mobile phones with MP3 playing function.