Analysis and research are made for the major national science and technology infrastructure project five-hundred-meter aperture spherical radio telescope(FAST). A new modeling approach which uses leakage features of gear pump and opening characteristic of pilot operated check valve to form a closed loop control is proposed to make the mathematical model more accurate. The prototype testing and testing equipment are designed to obtain flow-pressure coefficientK_q and opening characteristicK_f. Simulation model is established based on Matlab/Simulink to analyze the motion performance both in open and closed loop mode. And the mathematical model is validated by experiment. The results indicate that the mathematical model can describe the working principle of the actuator.K_qandK_fhave a good consistency with the experiment results,the actuator speed arises with the increase of input pulse in open loop and also can achieve stable track with changing load in closed loop. The maximum tracking errors of simulation and testing are 0.15 mm and 0.2 mm respectively and which can fulfill the designing accuracy. The system model can be used as the theoretical basis in subsequent research about FAST actuator and meanwhile as the reference of similar operating condition with major differences between protraction and retraction.