An electronic device includes an audio sensor, an audio output unit, a pulse width modulation (PWM) unit connected to the audio output unit, and a control chip. When the audio output unit outputs the audio signal, the audio sensor detects a volume level of the environment sound. The control chip determines a volume level of the audio signal according to the volume level of the environment sound and preset associations between volume levels of the audio signal outputted by the audio output unit and volume levels of the environment, and determines a duty cycle of the PWM unit according to the determined volume level and the maximum volume level. The control chip then outputs the duty cycle to the PWM unit, to adjust a current volume level of the audio signal outputted by the audio output unit to the determined volume level.