Abstract: This present invention provides a navigation system and a portable head up display thereof. The navigation system comprises a navigation apparatus and a portable head up display. The navigation apparatus is for generating a command with navigation message. The portable head up display is for receiving and processing the command with navigation message in wired or wireless manner, and then displaying the graphic data corresponding to the navigation message. Furthermore, the portable head up display is able to broadcast an acoustic data corresponding to the navigation message. Hereby, a user owning the personal navigation device (PND) can place this portable head up display in the vehicle, and the effectiveness of the navigation message displayed on the windshield can be achieved.