Abstract: The status and the progress of researches on flow characteristics of the regenerator in high frequency pulse tube refrigerator are described. The correlation equations and charts of the friction factor in some previous papers are discussed. The experimental condition and application range of these equations and charts are pointed out. It explains the reason why these is a great divergence in predicting the pressure drop in the oscillating flow regenerator when different equations and charts are cited in the optimum design of pulse tube refrigerators.