A Universal Serial Bus (USB) dock is provided. The USB dock includes: a plurality of downstream ports; and a upstream port, connecting the USB dock to a portable device, wherein the upstream port includes an On-the-go (OTG) ID pin and a differential pair; and a microcontroller, configured to detect operating states of the portable device, wherein when it is detected that the portable device is in a USB OTG host mode and has entered a suspend state, the microcontroller controls the portable device to switch from the USB OTG host mode to a USB device mode by toggling a state of the USB OTG ID pin, thereby charging the portable device via the upstream port.