A display apparatus is provided, which includes a USB Type-C connector, display panel, a multiplexing circuit, a switch circuit, and a display controller. The USB Type-C connector is connected to a portable device, wherein a USB signal between the display apparatus and the portable device includes an image-transmission channel and a data-transmission channel. The multiplexing circuit separates the image-transmission channel from the data-transmission channel. The display controller controls a display mode of the display panel. In response to the display panel being in a first display mode, the display controller transmits a control signal to the switch circuit to control the multiplexing circuit to switch to a first operation mode. In response to the multiplexing circuit being in the first operation mode, the portable device acts as a host terminal in the image-transmission channel, and acts as a device terminal in the data-transmission channel.