Abstract: The correlation of sound power with jet velocity is studied in this paper.It is indicated that Both Lighthill's and Lilley's formulas fit experimental data very well when Mach number of jet Maj>0 4,but the diviation between the results obtained from the formulas and experimental data is not so negligible as Maj<0 4.The authors propose substituting sixth power of the jet velocity instead its eighth power in the formulas.The direction sensitiveness and the frequency spectrum of jet noise have been investigated enperimentally.