Abstract: Basing on research works on steady jet noise reported by Maa,et al.,we studied the pulsed jet noise experimentally and theoretically further.Our investigation on a model of pulsed jet shows that the monopole representing the pulsation of exhaust air volume,and the quadrupole arises from the turbulence in jet as each is uncorrelated and can be reckoned separately,when the pulsating frequency is lower and the exhaust flow rate is much smaller than the production flow rate.The overall noise can be then abtained simply by summing up contributions of these two types of noise sources.Equations for the overall noise level and the spectrum density level have been derived.Having applied these equations to two models of pulsed jet,we found that they are adequate and can be used for scaling of the noise of reciprocating engines and pneumatic tools.