Abstract: An electronic hydraulic power steering system for automatically operating tractor is introduced in this paper. The control system includes steering controller and driving mechanism. A dual-channel Proportional Derivative(PD) control algoithm wasdevreloped for orientation tracking. The difference value between the expected angle acquired from the upper computer(that is, the computer for automatic drivecontrol) and the actual angle of the steering wheel was used as the input parameterof the controller. By the estimation of the turning direction and the regulationof PD control parameters, the impact on the steering system from the asymmetryof the cylinder can be compensated by the controller. Therefore both steeringoperations can obtain the same steering quality. Experimental results show thatthe control algorithm can avoid the asymmetrical problems and improve the stability, control precision and quick response of the system. It can be used asthe steering operator for automatic operation or assistant vehicles.