High power pulse xenon lamp is the core unit of inertial confinement fusion (ICF),whose luminous efficacy affects the output efficiency of ICF directly.The lamp transmittance is an important factor for the degradation of luminous efficacy.When high power pulse xenon lamp runs different shots,the transmittance of composite quartz tube will degrade.In this study,the middle of the composite quartz tubes was selected when the lamps run 0 shot,88 shots,2000 shots,3000 shots,5000 shots and 8000 shots,and the spectral transmittances of these samples were tested and compared.The transmittance has no longer a significant degradation when the xenon lamp runs 88~8000 shots.In order to find the reason for the degradation of the transmittance,the composite quartz tubes (middle tubes and the tubes closed to the cathode portion)of the xenon lamp that runs 0 shot and 2000 shot are selected,and then they are tested by the transmittance,X ray diffraction,fluorescence and component analysis.The testing results show that there is no crystal precipitation in composite quartz tube when the xenon lamp is running,so the degradation of the transmittance is not caused by the crystal precipitation;the valence change of cerium ion from cerium doped layer may be one reason for the degradation of the transmittance,the other reason is many impurities on the lamp tube from electrode.