The concept of pneumatically-driven split-Stirling-cycle cryocooler with clearance-phase.adjustor is proposed.It has the advantages of easy damping adjusting,low cost,simplifying manufacturing and assembling.The gap between the phase-adjusting part and the cylinder of spring chamber instead of dry friction acted on the pneumaticlly-driven rod is used to control motion damping of the displacer and adjust the phabe difference between the compression piston and displacer.A theoretical model for the clerance-phase-adjustor has been established and dynamic simulation of its operating performance at different gaps is demonstrated in this paper.The simulation resul are in good agreement with the experiment ones,therefore the theoretical model is feasible and reliable for the simulation.