The electro-hydrostatic actuator (EHA) is a kind of power-by-wire (PBW) actuator. In this paper, a typical architecture of EHA is described and the block diagram model of EHA is established directly from the mathematic equations without transfer functions, which is a nonlinear accuracy model. The influence of refeeding circuit on the EHA system is discussed based on the comparison with conventional linear model. A gain-variable PID controller is introduced to this model to compensate the friction.