A GM-type two-stage pulse tube refrigerator equipped with three rotary valves was developed, and the lowest temperature of 10.3K was obtained when lead shots were used as the second-stage regenerator material. From the measured pressure oscillation at both sides of the orifice plate connected to the pulse tube hot ends, the mass flow rate through the orifice was estimated and the equivalent PV work calculated. Based on the cooling capacity and calculated PV work, the refrigeration losses were found to depend on the temperature difference of the regenerator and showed a linear relation for both stages.