In some circumstances, huge mass, if not cushioned, may pull the piston to a halt at rod side or head side at ease with a tremendous velocity causing huge impact. As a result of this issue, the boom cylinder of hydraulic excavator provides cushioning apparatus at the rod side stroke end. This paper discusses and analyses the cushioning apparatus structure of boom cylinder, and then proposes a numerical simulation model with SimulationX. It is known to us that many dynamic parameters of boom cylinder vary as mechanical structure or motion of excavator attachment changes. Thus in order to study the relationship between kinetic parameters and cushioning capability of boom cylinder, an excavator attachment model is built next. The last part of this paper is devoted to the obtained simulation results.