Abstract: In order to obtain a further understanding of the cavity aeroacoustics and test the noise suppression effect using a saw tooth spoiler, aeroacoustics characteristic over an open cavity with a length to depth ratio of 5:1 at Mach 0.85 are investigated in the present study. The CFD simulations are performed by delayed detached eddy simulation (DDES) based on Spalart-Allmaras one equation turbulence model. The results obtained from clean cavity prediction are compared with experimental sound pressure level (SPL) data from QinetiQ, UK. It can be observed from the results that the tone amplitude of the 2^nd and 3^rd dominant modes are generally well predicted (within 2 dB), whilst the 1^st and the 4^th tones are not so well resolved. In order to evaluate leading-edge spoiler which is widely used as a passive control method on cavity noise suppression, the main focuses are sound pressure level of cavity with a leading-edge saw tooth spoiler. According to the comparison of computational SPL results between cavity with spoiler and clean cavity, the saw tooth spoiler reduce the 2^nd dominant tone amplitude over 10dB, and the over-all SPL about 5dB, significant noise suppression effect for open cavity is validated.