Abstract: Abstract: In the tractor suspension, previous research mainly focuses on the leveling or attitude adjustment in the single hydraulic cylinder or rotary cultivator. In order to design a kind of double hydraulic cylinder for the hydraulic adjusting system, this paper proposed the three point of hitch system for the medium horsepower hills mountain tractor using the fuzzy PID control algorithm of adaptive angle, while the simulation analysis and bench tests were conducted to design the horizontal posture adjusting hydraulic system. A bilateral three-point suspension adaptive structure of hydraulic cylinder was developed to improve efficiency of the conventional three-point tractor suspension, for better adapting to the hilly mountain complex operation requirements. Firstly, in a kinematics analysis on the lifting arm, lifting rod, agricultural tools tripod and other components, MATLAB software was used to simulate the displacement and the inclination angle of the hydraulic cylinder, when the transverse inclination angle was -15°, 15°. Due to the interference and freedom limitation of three-point suspension of the lifting rod, the relationship between the displacement and angle of the hydraulic cylinder piston rod can only be linear model within ±15°. In the process of the lifting tilt, the asymmetry of the hydraulic cylinder can lead to the deviation of the center of farming tools and the change of the ploughing depth, so the ploughing depth should be compensated. Secondly, the hydraulic system of lateral pose adjustment mechanism of the quantitative pump was designed to establish the mathematical model of the hydraulic system based on state space. The hydraulic system of horizontal attitude adjusting system was simulated in Simulink under the control of the fuzzy adaptive setting PID method, where the input signal to voltage signal, a given voltage within 0-12 V, the angle of 10 ° and 15 °, the stroke of hydraulic cylinder of 100 mm, the step time of 2 s, the simulation time for 5 s. Finally, the simulated results after the tractor suspension horizontal posture adjustment were compared with the experimental data based on five character TS404-h tractor suspension system control experimental platform, with the maximum error of 1%, the average error of 0.7%, where the adjustment time of simulation system was less than 0.2 s, the adjustment of the test time was about 1s, the overshoot of experiment and simulation was 0, the stable time was around 0.1 s. Due to the instability and measurement error of the three-point rear suspension mechanism, the collected data from the test showed the serious oscillating at the initial stage, which can be caused by the interference of the three-point suspension hinged components, but the overall trend was consistent with the simulation results. The findings showed that the rear suspension mechanism can be quickly adjusted to the set angle within the predetermined target (within the range of ±2°-±15°), which can meet the requirements of transverse angle adjustment for mountain and hill operations.