Abstract: The requirement of high efficiency cooling method at 20 K temperature range plays an important role in the growing demand of aerospace refrigeration capacity. Stirling/pulse tube hybrid cryocooler shows great potential to achieve efficient refrigeration in 20 K temperature range. As the key component of the hybrid cryocooler,the regenerator greatly affects the overall cooling capacity of the cryocooler. So a reasonable design method is essential for ensuring the performance of the regenerator. Because of the difference between the thermodynamic properties of helium and regenerative material in 20 K temperature zone and that in higher temperature zone like 80 K,the design method for the regenerators working at rather high temperature zone cannot be simply applied. A dedicated design method and process for the 20 K regenerator is presented in this manuscript. By using the regenerator simulation software Regen3.2,parameters such as the average pressure,phase angle,cold end pressure ratio and packing type are optimized to achieve the highest COP. With the optimal design,the regenerator could reach a COP of over 0.035 and cooling capacity of 0.5 W at 20 K. This design of the regenerator presented in this manuscript lays a solid foundation for the further development of the high efficiency Stirling/pulse tube hybrid cryocooler. The presented method could also be used for the design of regenerators working at similar temperature range.