In order to satisfy the requirements of high frequency and large stroke in the hydraulic actuator of free piston generator (FPLG), a nonlinear feedforward controller for a hydraulic actuator was designed and driven by multistage servo valve. A double acting hydraulic operated piston and a proportional servo valve driven by a three stage were mainly included. The feed forward controller combined with traditional feedback control method, and inversion model to produce the feedforward control algorithm based on, considered the prediction of the system load conditions, the feedforward controller was acept of hydraulic actuating device under the prediction of dynamic load as input for tracking expected trajectory of the optimal input signal. The simulation tests verify the effectiveness and practicality of the proposed controller, which can meet the needs of the development of the FPLG.