Abstract: Trunked mobile radio system has the capacity of dispatching through voice, but dose not have the capacity of location and navigation. GPS (Global Positioning System) has the capacity of location and navigation but dose not have communication links between users. So, it is of signification to realize automatic vehicle location and dispatching system, which remedy their defects and absorb their quintessence, by organically integrating trunked radio system with GPS . Based on the analysis about Motolora's SmartNet trunked radio system, the authors point out some key techniques to realize the system. Those are how to distinguish control signal and voice for establishing stable GPS data link and balance channel load etc.The experiment results have proved out our means.