The problems of variable load and external interference exist in the hydraulic control system of large series manipulator. The equivalent mass of the manipulator with different working posture will cause change of the natural frequency of the hydraulic cylinder system and affect the dynamic characteristics of the system. Therefore, a sliding mode control strategy based on the linear extended state observer (LESOSMC) was proposed.The research object was the demolition robot manipulator.The simulation results show that LESOSMC has good dynamic characteristics and steadystate accuracy when the manipulator is in different posture, and has good tracking performance for periodic sinusoidal signal.LESOSMC has good robustness in variable load control of the manipulator, which meets the requirements to joint position control of the heavyduty hydraulic manipulator.It provides an effective engineering method for solving the joint position control of the hydraulic cylinder of the heavyduty hydraulic manipulator.