An advanced hydrostatic actuation system referred to as the Electro Hydraulic Actuator (EHA) has been designed and prototyped. The prototype of EHA exhibits a very high level of dynamic performance and positional accuracy. EHA’s positional accuracy with a simple outer-loop proportional controller equals its optical position-encoder resolution of 10 Micron. In this paper, a linearized mathematical model of EHA is derived and used as a basis for model identification. Open loop experiments and numerical optimization are used for tuning some of the unknown model parameters and for quantifying their influence. The resulting model is validated and matches closely the measured response.