Abstract: Considering the characteristics of the servo system, such as disturbance, nonlinearity and high inertia, variable structure controller(VSC) based on extended state observers(ESO) are designed for the aim of quick, stable and high-accuracy controlling processes. The disturbances and high-order factors are estimated and compensated using ESO. Dynamic compensation reduces the motion system to approximately a triple integrator which can be easily controlled using VSC. Because ESO provides a high-frequency path for the dynamic state not modelled, the chatter of VSC is reduced. Through tests in the gun turret system, it was shown that this controller is superior to the engineering PID and general VSC.