Abstract: A Dongfanghong-X804 tractor was used as a platform and an automatic steering controller based on double closed-loop control was developed to realize autonomous navigation of agricultural machinery.The make-up of the whole steering system and the working principle are presented: using an angle sensor KMA199 to measure steering angle and a gyroscope integrated in ADIS16300 to measure angular rate.In order to realize servo control of steering system, electro-hydraulic valves, shift solenoid valve and relief valve were used as actuators for automatic steering.Then the mathematical model of steering system was derived and the hardware circuit realization was described with CAN network design.According to characteristic of the system nonlinear, the transfer function between the proportional valve input current and steering angular can be seen as a second-order inertial part and a latency part, and a double closed-loop control algorithm for steering system was designed, using Matlab System Identification Toolbox to estimate transfer function parameters.Finally, tests were conducted to examine the steering system, including a calibration test for ADIS16300, which indicated the high accuracy of ADIS16300 angular velocity integral values, with the average error of 0.53°; and a test of the steering control system was carried out to verify the performance of double closed-loop control algorithm, which showed that the steering control system solved the control overshoot well and the average error is 0.4°, with 1.3 s tracking time; the average angular rate tracking error is 1.25 °/s, with 0.2 s tracking time.