A high-speed data transmission interface circuit used in a network switch device is provided. The high-speed data transmission interface circuit comprises a main circuit hoard, a connector and a daughter circuit board. The main circuit board comprises a transmission port interface module and a first wire. The transmission port interface module comprises a reduced pin extended attachment unit interface (RXAUI). The first wire connects the connector and the main circuit board. The daughter circuit board comprises a high definition multimedia interface (HDMI) module and a second wire. The HDMI module is connected to an external network device through a HDMI signal wire. The second wire connects the connector and the HDMI module. The transmission port interface module communicates with the external network device through the connector and the daughter board.