Aiming at the problem of unbalanced flow supply caused by nonlinear characteristics and external disturbance in direct drive electro-hydraulic servo system, based on active disturbance rejection control theory, a hydraulic cylinder position control method based on third-order linear active disturbance rejection control was proposed to realize the closed-loop control of motor speed and hydraulic cylinder position in direct drive electro-hydraulic servo system.Meanwhile, aiming at the problem of poor control effect caused by imprecise modeling of traditional system, based on theoretical analysis, combined with the performance and actual working conditions of electro-hydraulic servo system, the AMESim simulation model of direct drive servo hydraulic system was established.The co-simulation model of AMESim and Simulink was established to verify the effectiveness of the controller. The results show that the control strategy can be used to effectively eliminate the displacement fluctuation caused by the unbalanced flow supply, and the average absolute percentage error of hydraulic cylinder displacement is 4.4%, so a good position tracking can be achieved.In the case of external load disturbance, the system has strong anti-interference ability to ensure the stability of the system.