Init ial shock wave ( ISW) generated by engine ex hausted flow f ield has harmful effect on launch equipment so measures should be taken to attenuate this ef fect. As one of these measures a perforated attenuator was int roduced to repress ISW. Experiment w as conducted to compare the eff iciency of ISW at tenuators with dif ferent perforation rat io. Ex perimental engine w as used in the study. Pressure of ISW on rigid arc w as measured w ith piezo- resistance pressure transducers. Pressure data w ere analyzed by w avelet transform in w avelet domain. Frequency band energy spect rum and intensity index of ISW based on wavelet coef ficient were obtained. Peak pressure attenuat ion eff iciency and intensity index attenuation eff iciency w ere def ined to evaluate the funct ion of attenuator. Result show s that the attenuator is quite perfect to repress ISW, and lower perforat ion rat io has better at tenuation function in near f ield for rocket eng ine.