The main function of vehicle carriage locating terminal is introduced along with the working principle of the system and composition of Open AT developing tools. the hardware design of vehicle carriage locating terminal and the modular design of system software are stated. The functions of the main programs, the system control modules and every sub-module are described. The working principle block diagram, the hardware structure block diagram, the initialized program flow chart of the system control module and the flow chart of the timer interrupt processing function are given.