A radio navigation system for use with an automobile audio device is provided. The radio navigation system includes a positioning receiver having a modulation transmitter and receiving a positioning signal, wherein the modulation transmitter converts the positioning signal into a modulated signal and then transmits the modulated signal; a demodulation receiver mounted in the automobile audio device, receiving the modulated signal and converting the modulated signal into a voice signal to the automobile audio device; and an output device outputting the voice signal and the positioning signal.