Abstract: A transmitting and conversion apparatus for universal serial bus (USB) to high definition multimedia interface (HDMI), comprises main body, at one end of the main body, there is a USB connection port, while there is a HDMI output port at the another end; in the main body, there is a USB interface, a USB Hub circuit, a USB to 12/24-bit RGB format output circuit, a USB audio signal conversion circuit, a HDMI conversion circuit and a micro-computer unit (MCU). By using the subject apparatus, the USB connection port can be connected to the interface port of a computer main frame, the computer main frame then outputs a USB packet video signal sequentially via USB Hub circuit, USB to 12/24-bit RGB format output circuit, USB audio signal conversion circuit, HDMI conversion circuit and convert the signal into signal of HDMI format, and finally, the signal of HDMI format is outputted via a HDMI output port for displaying.