Electrohydraulic steering gear systems drove directly by servomotor have a characteristic of high nonlinear degree, low response and vulnerable to external load disturbance. Traditional PID controller cannot resist interference. Moreover, with working condition changing, control effect becomes poor. In order to overcome the shortcomings of the traditional PID controller, the transition process was arranged to adjust the system’〖KG-*3〗s response process and reduce the dynamic impact at the startstop process. The expansion state observer (ESO) was designed to estimate and compensate the hydrodynamic load disturbance. Furthermore, the response speed of the system was increased through the combination of nonlinear control law. Based on the design of active disturbance rejection controller (ADRC), MATLAB and AMESim cosimulation research was adopted. Compared with the traditional PID controller, the results show that the startstop process controlled by active disturbance rejection technique is smoother, and the system’〖KG-*3〗s antiinterference ability is further enhanced.