The effect of length-depth ratio (L/D) on flow and aeroacoustic characteristics of cavity is studied using detached eddy simulation (DES) based on Realizable k-εturbulent model. The cavity is 0.508m long by 0.1016m and the depth is variable to obtain L/D ratio of 3,5,8,14,17. The Mach number is 0.85 and the Reynolds number is 6.84 × 106. The results indicate that L/D is significant on the pressure gradient and aeroacoustics, and the flow type changes gradually from open cavity flow to closed cavity flow with the increase of L/D. In addition, static pressure, fluctuating pressure and aeroacoustic characteristics must be considered when defining cavity flow types.