Stirling type pulse tube cryocoolers (SPTC), typically operating at 30–60Hz, have the advantage of compact structure, light weight, and long life compared with Gifford–McMahon type (1–2Hz) PTC (GMPTC). The behavior of flow and heat transfer in the regenerator of a 4K SPTC deviates from that at warmer temperatures and low frequencies. In this paper the behavior of 4K regenerator at high frequencies is investigated based on a single-stage 4K SPTC precooled by a two-stage GMPTC. The 4K SPTC and the GMPTC is thermally coupled with two thermal bridges. The 4K SPTC uses a 10K cold inertance tube as phase shifter to improve phase relationship between mass flow and pressure. The regenerator void volume is an important factor that significantly influences the heat transfer between regenerator matrix and working fluid helium, pressure drop along the regenerator, and phase shift between mass flow and pressure. In this paper, influence of regenerator void volume on the performance of the 4K SPTC with different operating parameters including operating frequencies and average pressure is studied theoretically and experimentally. The first and second precooling powers provided by the GMPTC are obtained which are important parameters to evaluate the efficiency of the whole 4K system with precooling. The results of the regenerator void volume are given and discussed in normalized form for general use.