Active Disturbance Rejection Control (ADRC) is widely applied in automatic machines, like electric motors, proved effective in performance enhancement. However, there is little report in its application in Electro-Hydrostatic Actuators (EHAs), where hydrostatics and power electronics coupled heavily. This paper gives both theoretical and experimental study on ADRC application in an EHA for the thrust vector control of a launcher. The mathematical model and state space model of the system were established and the system disturbances were estimated and compensated. The performances were compared to the counterpart using traditional proportional-integral-differential (PID) algorithm. It shows that ADRC is more effective than PID in rejecting system disturbances and model uncertainties，significantly reducing tracking errors and improving EHA dynamics.

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