A multiplexing circuit, comprising a first switch circuit, a second switch circuit, a third switch circuit, and an isolation circuit, wherein the multiplexing circuit has a first external transmission end (USB_DP), a second external transmission end (USB_DN), a right-channel transmission end, a left-channel transmission end, a first internal transmission end (USB_DP_1), a second internal transmission end (USB_DN_1), a first on voltage end (VOUT1), a ground end, and a second on voltage end (VOUT2), wherein the first switch circuit is separately coupled to the first external transmission end (USB_DP), the right-channel transmission end, and the first on voltage end (VOUT1), and the first switch circuit is configured to: receive a first on voltage output by the first on voltage end (VOUT1), and transmit, to the first external transmission end (USB_DP), a right-channel audio signal provided by the right-channel transmission end; the second switch circuit is separately coupled to the second external transmission end (USB_DN), the left-channel transmission end, and the first on voltage end (VOUT2), and the second switch circuit is configured to receive the first on voltage, and transmit, to the second external transmission end (USB_DN), a left-channel audio signal provided by the left-channel transmission end and characterised by the isolation circuit is separately coupled to the third switch circuit, the first on voltage end (VOUT1), the ground end, and the second on voltage end (VOUT2), and the isolation circuit is configured to: when a second on voltage output by the second on voltage end (VOUT2) is received, but the first on voltage output by the first on voltage end (VOUT1) is not received, transmit the second on voltage to the third switch circuit; and the isolation circuit is further configured to: when the first on voltage and the second on voltage are received, pull down the third switch circuit, and isolate the ground end from the second on voltage end (VOUT2); and the third switch circuit is further separately coupled to the first external transmission end (USB_DP), the second external transmission end (USB_DN), the first internal transmission end (USB_DP_1), and the second internal transmission end (USB DN_1), and the third switch circuit is configured to: when the second on voltage is received, couple the first external transmission end (USB_DP) to the first internal transmission end (USB_DP_1), and couple the second external transmission end (USB_DN) to the second internal transmission end (USB_DN_1); and the third switch circuit is further configured to: under the pull-down effect of the isolation circuit, disconnect the first external transmission end (USB_DP) from the first internal transmission end (USB - DP _1), and disconnect the second external transmission end (USB_DN) from the second internal transmission end (USB_DN_1). the first switch circuit is separately coupled to the first external transmission end (USB_DP), the right-channel transmission end, and the first on voltage end (VOUT1), and the first switch circuit is configured to: receive a first on voltage output by the first on voltage end (VOUT1), and transmit, to the first external transmission end (USB_DP), a right-channel audio signal provided by the right-channel transmission end; the second switch circuit is separately coupled to the second external transmission end (USB_DN), the left-channel transmission end, and the first on voltage end (VOUT2), and the second switch circuit is configured to receive the first on voltage, and transmit, to the second external transmission end (USB_DN), a left-channel audio signal provided by the left-channel transmission end and characterised by the isolation circuit is separately coupled to the third switch circuit, the first on voltage end (VOUT1), the ground end, and the second on voltage end (VOUT2), and the isolation circuit is configured to: when a second on voltage output by the second on voltage end (VOUT2) is received, but the first on voltage output by the first on voltage end (VOUT1) is not received, transmit the second on voltage to the third switch circuit; and the isolation circuit is further configured to: when the first on voltage and the second on voltage are received, pull down the third switch circuit, and isolate the ground end from the second on voltage end (VOUT2); and the third switch circuit is further separately coupled to the first external transmission end (USB_DP), the second external transmission end (USB_DN), the first internal transmission end (USB_DP_1), and the second internal transmission end (USB DN_1), and the third switch circuit is configured to: when the second on voltage is received, couple the first external transmission end (USB_DP) to the first internal transmission end (USB_DP_1), and couple the second external transmission end (USB_DN) to the second internal transmission end (USB_DN_1); and the third switch circuit is further configured to: under the pull-down effect of the isolation circuit, disconnect the first external transmission end (USB_DP) from the first internal transmission end (USB - DP _1), and disconnect the second external transmission end (USB_DN) from the second internal transmission end (USB_DN_1).