Abstract: The tractor steering system is the key to ensure the safe and efficient operation of the driving mechanism, the traditional hydraulic steering system in the steering process is prone to heavy steering and even failure, and the performance is not ideal, so this paper put forward a new hydraulic steering-by-wire system, which combined hydraulic steering technology with the steering-by-wire technology. This system not only cancels the steering wheel and the mechanical connection between the hand wheel and the steering gear, but also simplifies the hydraulic oil circuit design between the steering gear and steering wheel. It makes steering flexible and convenient, and meanwhile the use of hydraulic system can ensure high power output. Agricultural vehicles need to drive on the highway when transferring in the different regions, and its center of gravity is generally higher, while its speed is lower compared with the passenger vehicle. Actually, the speed is high in their own condition, and the vehicle's lateral stability is poor. When the agricultural vehicle is in operation, the driver needs to steer the wheel frequently, but the design of the variable angle transmission ratio and variable force transmission ratio of hydraulic steering-by-wire system makes the vehicle handling stability improved, and can reduce the driver's labor intensity effectively. Compared with the traditional full hydraulic steering system, the new system can better promote the development of agricultural vehicles, and eventually make the unmanned autonomous operation agricultural vehicles come true. This paper introduced the overall design of the tractor's hydraulic steering-by-wire system, and all kinds of important parts were showed clearly by design chart: ECU (electronic control unit), circuit design, input signal, output signal, and so on. The system uses the classical PID (proportion, integral, derivative) to design the controller, and the whole system is a closed loop control system. Building model and simulation analysis were based on Simulink/Simhydraulic module of MATLAB software, and the modeling and the real vehicle modification for various parts were all based on the overall design principle of hydraulic steering-by-wire system. After the completion of the selection of parts, the tractor was modified. The key components of the new system and the design of the circuit and controller were described in detail, which were compared with the original structure of the steering system. Meanwhile, the energy saving of the new system was analyzed in this paper. Then the static and dynamic experiments with the prototype were finished. The static experiment was a random rotation experiment, the main purpose of which was to test how the new system was feasible, and ensure that the dynamic experiments could be carried out safely. Four dynamic experiments were snake-shaped experiment, lemniscate experiment, steady-state experiment, and angle transient response experiment, which were used to evaluate different vehicle performances. Every experiment tested the hydraulic steering system and hydraulic steering-by-wire system respectively, and the 2 systems' difference was evaluated in the performance of steering sensitivity, handling stability, and convenient operation. In the experiment process of 2 systems, 2 kinds of data should be obtained, i.e. the hand wheel angle data (the theoretical angle data) and the steering wheel angle data (the actual angle data). Two kinds of data were compared and analyzed, and the experimental results showed that the theoretical and actual angle curve of hydraulic steering-by-wire system fitted better, and the error was lower than the full hydraulic system. Although both of the 2 steering systems could complete the steering action, the difference of performances existed between the hydraulic system and hydraulic steering-by-wire system. Hydraulic steering-by-wire system is feasible, which makes the function innovation, structure innovation, and practice innovation. In function, it combines the advantages of steering-by-wire technology and hydraulic technology, so that the tractor steering performance gets a new upgrade. The system structure innovation is to use various types of sensors to complete the closed-loop control, use electromagnetism proportional servo valve to replace the full hydraulic steering gear, and use the PID to controller complete steering system control. Based on theory design, we modified the tractor, and performed a series of experiments with the tractor. The final experiments results showed that the hydraulic steering-by-wire system can achieve better steering function compared with the traditional full hydraulic steering system.