The thermodynamic loss of rotary valve and the coefficient of performance (COP) of GM-type pulse tube coolers (VTCs) are discussed and explained by using the first and second laws 0f thermodynamics in this paper The COP 0f GM-type PTC，based on lwo types of pressure profiles the sinusoidal wave inside the pulse tube and the step wave at the compressor side has been derived and compared wim mat of Stirling-type PTC Result shows that additional compressor work is needed due to the irreversible entropy productions in the rotary valve thereby decreasing the COP of GM-type PTC The eriect of double—inlet mode on the COP of PTC has distinct improvement at lower temperature region (larger TH/TL). It is also shown that the COP of GM-type PTC is independent of the shape of the pressure profiles in the ideal case of no flow resistance in the regenerator.