Audio output system and control method thereof

The invention relates to an audio output system. The audio output system comprises a reference voltage generation circuit, an output-stage circuit, a switch, a charge pump circuit and a control circuit; the reference voltage generation circuit provides reference voltage; the output-stage circuit generates an audio output signal according to the reference voltage and a first signal; the switch is coupled between the output end of the output-stage circuit and a grounding terminal; the charge pump circuit outputs bias voltage so as to bias the output-stage circuit; the control circuit is coupled to the switch, the charge pump circuit and the reference voltage generation circuit; the control circuit provides a first control signal to control the switch, provides a second control signal to control the charge pump circuit, and provides a third control signal to control the reference voltage generation circuit; in the starting operation, the control circuit enables the first control signal to conduct the switch, so