Free-piston Stirling cryocoolers operate without physical linkages. They rely only on the gas pressures to make the correct motions of the reciprocating elements. The estimation of the pressure drop across a regenerator is very crucial in analyzing dynamic motion of the expander and predicting the performance of the cryocooler. This thesis proposes a new model of the pressure drop for more accurate description of oscillating flow in contrast to an existing model based on steady flow. To validate the new model, the analysis of dynamics of the Stirling cryocooler is carried out. For the universal uses of the oscillating flow model, non-dimensional parameters are derived from capillary tube model of the regenerator prior to experiments. And correlation equations of the model are obtained from the experiments for three types of wire-screen regenerator under various operating frequencies and inlet mass flow rates. These equations shall be useful for not only Stirling cryocooler but also pulse tube refrigerator design.