Abstract: A flexible chassis system with full hydraulic driving was put forward in order to meet the demand of plant protection practice under the complex agricultural and forestry environments. For the nonlinear hydraulic control system of the four-wheel driven chassis through valve-controlled hydraulic motors, the state equation of the system was established. The system stability was analyzed with Lyapunov theory, and the Monte Carlo simulation method was used for system reliability prediction and optimization. Results showed that the hydraulic control system was stable and the reliability was high. The mean reliability value was 0.89 after optimization and the forecast value of the mean time before failure was 8 526 h, which was far above the work time of 2 160 h within a year for the chassis. The AMESim software was used for modeling and simulating the hydraulic control system and the results were compared with prototype experiment results. The results showed the system stability was high when PID controller parameters was set as K_P=0.5,K_I=4,K_D=0. At the above conditions, system response was quick and system reached stable state after 2.5 seconds. There were slight fluctuations in the wheel acceleration response curve. But the oscillation frequency was within 2 times. The output curves of motor speed were almost overlapped when load disturbance torque was increased from 1 Nm to 20 Nm. This demonstrated that the robustness of hydraulic system was good and its reliability and stability met the chassis demand.