When the vehicle with optical seeker in its head side window flights at high speed in aerosphere, cavity flow phenomena occurs. So, the high-precision LER/RANS hybrid algorithm model is established to solve supersonic flow. The Settles three dimensional carity′s supersonic flow is studied. And then, on the basis of accurate numerically calculated flow-field data, the optical transmission effect of the cavity shear layer region is researched. The results show that, the shear layer structure of cavity flow will cause light jitter, lead to severe wave-front distortion, reduce light intensity Strehl ratio significantly, and reduce the accuracy of the optical guidance.