Abstract: Aero-optic effect is investigated in supersonic/hypersonic flow. Flat plate, ramp and cave model in supersonic/hypersonic flow condition are studied with large eddy simulation (LES). Turbulent density pulse is predicted to verify coefficient of density pulse model-mixing length (ML) model. It indicates that LES method simulates turbulent density pulse well in flat plate boundary layer flow, oblique shock wave/boundary layer interaction and strong separation flow. Density pulse data obtained by LES is used to verify ML coefficient and set a quantitative result. The modified ML was used to predict aero-optical effect on missile successfully.