Abstract: Combined the theories of thermodynamics and thermoacoustics,the structure of the pulse tube-one of the most important components in the pulse tube cryocooler-was analyzed.The function of the structure of pulse tube in the distribution of the gas temperature and pressure along the tube has been found. Two kinds of the tapered pulse tube structures have been proposed accordingly in this thesis and have been investigated numerically. It has been found that there is an optimum cone angle for the tapered pulse tube cryocooler. When the pulse tube cryocooler works on this optimum cone angle,the performance can be improved.The convergent and the divergent tapered pulse tubes were submitted and validated in the numerical simulation and the experiment.