The performance of automatic steering control directly affects the accuracy of tractor navigation. In order to improve the tractor navigation performance, the tractor automatic steering control technology is researched. The automatic steering control system for the full hydraulic steering tractor is designed with the Lovol Europard FT704 tractor. The mathematical model of automatic steering system is established. The PID parameters are determined by digital simulation analysis, and verified by steering test. The field test results show that the offset error is not greater than 5.98 cm and the average offset error is not greater than 1.23 cm at the travel speed of 1.0 m/s. The field tests indicated the tractor automatic steering control system can meet the needs of tractor automatic navigation.