Abstract: Navigation control system based on RTK-DGPS for Dongfanghong X-804 tractor was developed. The system includes RTK-DGPS receiver, navigation controller, steering controller, electrohydraulic steering actuator and encoder sensor for the steering angle testing. The closed control loop of the steering angle is composed of steering controller, electrohydraulic steering actuator and encoder sensor. The closed loop can realize the servo control of the steering angle according to the control command from navigation controller. The control transfer function model was developed for straight trajectory tracking based on tractor kinematics model and the steering control system. The input of the transfer function is lateral tracking error and the output is commanded steering angle from navigation controller. The navigation controller was developed using PID algorithm. The stability and the responding capability of the control system were discussed and analyzed, and the control parameters were optimized. According to the characteristics of high turning radius of the tractor, a headland turning mode through spanning lines was used in the navigation control system for the tractor. The field tests showed that the maximum offset error was less than 0.15 m and the average offset error was less than 0.03 m for straight trajectory tracking at the traveling speeds of 0.8 m/s. The field tests indicated that the proposed headland turning control method is appropriated to Dongfanghong X-804 tractor.