An automotive on-board diagnostic (OBD) computer system with an audiovisual guiding function includes an OBD main unit and a transmission connector. The OBD main unit includes a transmission port, a control unit, a receiving unit, a guide light, a sound unit, and a first sensing unit. The transmission connector includes a control module, an illumination unit, a transmitting unit, and a second sensing unit. Once activated, the control module not only turns on the illumination unit to provide illumination light, but also drives the transmitting unit to send a control signal to the receiving unit of the transmission port, in order for the control unit to turn on the guide light and the sound unit according to the control signal. The guiding light and instruction sound provided respectively by the guide light and the sound unit can help the user locate the transmission port.