Aiming at the problems of unstructured and complex hilly orchard environment and low efficiency of conventional weeding methods, an orchard weeding robot chassis system was proposed.According to the hilly terrain and landform environment of the orchard, the vehicle body control mode and the overall structure scheme of the weeding robot chassis were determined, mainly including the hydraulic transmission system, and electrical control system, etc. With motion control as the core, in order to improve the control accuracy of the hydraulic system, the supporting electrical control system, remote control receiver and CAN communication protocol of the weeding vehicle were designed, which were composed of the main controller, remote control receiver, motor drive module and navigation module, and the software flow was determined. The motion controller was designed based on the active disturbance rejection control algorithm. The robot track speed was determined by the valve angle of the hydraulic system, it can be seen that the dynamic performance of the motor directly connected to the control valve was the motion control target. The Simulink simulation model was established by taking the motor angle of the hydraulic valve as the object and the speed, disturbance and output as the state variables. The simulation results showed that the ADRC reduced the adjustment time by 0.42s, the overshoot by 11.5% and the stability time by 0.14s compared with the PID control. Ground experiments were arranged to verify the effectiveness of the robot system. The experiments showed that the average walking speed of the weeding robot using active disturbance rejection control combined with navigation function was 6.2km/h, the mean square deviation was 0.037km/h, the operation efficiency was 0.51hm2/h, and the average effective weeding rate was 97.46%. It can walk normally on a 25° slope, and the standard deviation of tracking error for the navigation path was 4.732cm. The motion control response was timely, which can improve the safety and accuracy of weeding operation.