An automatic navigation system was developed on XDNZ630 rice transplanter using RTK-GPS technology. The steering mechanism, gear change mechanism and transplanting mechanism of the rice transplanter were modified from manual control system to electronic control system by using servo motors. According to the position information of the rice transplanter acquired from GPS receiver and vehicle sensors, the close-loop feedback control system of steering was built. The system can accurately control rice transplanter to follow row navigating and turn around at the end of the field by PID tracking method. The road and field experimental results indicated that the lateral tracking error could be kept within 10 cm when the speed of the rice transplant was not greater than 0.6 m/s. The control system can completely satisfy the precision requirement of rice transplanting. 