Focus on the trajectory planning problem of shovel operations of skid steer loader, a trajectory curve fitting equation is established. By use of the robotics theory and the D-H method, the functional relationship between the kinematics of the working device of skid steer loader and the displacement, position and orientation of boom bucket cylinder is derived, and the driving equation of displacement cylinder is obtained. Based on the requirements of precise trajectory control, an electro-hydraulic proportional position control system for position and orientation control is designed and the state equation of the system is established. By using fuzzy self-tuning PID control algorithm, the outside interference, parameter uncertainty and the error caused by other factors are weakened. The trajectory tracking simulation results demonstrate that: the biggest shovel tracking error is 12.5mm, the designed electro-hydraulic proportional control system can effectively track the trajectory of the working device of skid steer loader in automatic digging process. The rightness of the established model and the effectiveness of the corresponding controller are also proved.