Abstract: This paper presents effects of different boundary-layer thickness to cavity depth ratios on sound pressure level（SPL） distributions and sound pressure frequency spectrum characteristics（SPFS） inside the open cavity with length to depth ratio of 8.The data presented herein was obtained over Mach numbers of 0.6 and 1.5 at a Reynolds numbers of 1.23×10⁷ and 2.26×10⁷ per meter.The results show that decrease in ratios of the boundary-layer thickness to the cavity depth（δ/D） leads to increase in SPL on the different position measurement inside the open cavity.It also causes intense interaction of the shear-layer over the cavity and flow in the cavity or cavity rear-wall,which leads to increase in SPL at different discretized frequencies for measurement positions in the cavity.Generally,decrease in δ/D leads to flow self-oscillations and aerodynamic noise which have adverse influences on cavities and internal weapon’s structural vibration.