This research presents a dynamic analysis of a large-scale hydraulic cylinder actuator via numerical simulation. A model of the actuator built with dynamically parameters is implemented basing on fluid mechanics and vibration theories. In which, coefficients of viscous damping and stiffness generated by compressibility and viscous characteristics of hydraulic oil are considered. Hence, the large-scale hydraulic cylinder actuator can be investigated via an equivalent model of mass-spring-damper. In order of obtaining the system response, numerical simulation is done with some realistic actuator parameter sets. The results are consistent with reality and can be used as valuable fundamental for large-scale hydraulic cylinder actuator design.