Abstract: Increasing cooling capacity on the premise of lightweight is an important trend in pulse tube refrigerator technologies.A coaxial high frequency pulse tube refrigerator working at liquid nitrogen temperature with a mass of only 5.7 kg is reported.The design parameters of its main structure and the cooling performance are introduced.After optimization by inertance tube phase modulation, a cooling capacity of 25 W can be generated at 80 K when the temperature of the hot exchanger is 293 K, the operating frequency is 74 Hz, and the input power is 500W.It is experimentally investigated how the compressor efficiency, the relative Carnot efficiency of the cold finger, and the phase shift between the mass flow and pressure wave at the inlet of the cold finger, change with the size and frequency of the inertance tube.Analysis reveals that when the optimal working frequency of the compressor is close to the optimal working frequency of the cold finger, the mass flow phase angel ahead of the pressure wave phase angel about 30° at the inlet of the cold finger.