Abstract: A portable pulse fogger, in which the fog will be generated by inducing pesticide into the pulse-jet engine exhaust tube that is full of high temperature and high speed exhaust gas, can be applied in disease and insect controling in forestry, greenhouse and sanitation with the advantages of high application efficiency and low environmental pollution. A system for measuring the gas-flow fluctuation velocity was set up to obtain the pressure signals at different axial positions of exhaust tube. On the principle of correlation between pressure signals from one signal source, the correlation analysis of two pressure signals at various positions of exhaust tube had been carried out. The autocorrelation function chart showed that the pressure signals in the exhaust tube were characterized as the sinusoidal or the cosinoidal waves with a few of random signals. The average gas-flow fluctuation velocity was derived from mutual correlation analysis of two signals at two positions. The average maximal gas flow velocity obtained by this measuring system was 5883 m/s, which was 8.72 times as fast as local sonic velocity 669 m/s.