11cm。 According to the specifications of ISO 11783 standard, an automatic navigation control system was built. In the system, there were five ECUs, and the hardware and software design of steering control ECU were described in detail. At last the network service performance of the navigation control system was analyzed, and line path experiments were finished with the designed navigation control system. Experiments indicated that tractor navigation control system can satisfy the need of real time and could realize line path tracking. The lateral error is less than 11cm tractor tracking line path at a speed of 1m/s.