Conformal dome may enhance the velocity and effective range of the missile systems by providing better aerodynamical surfaces than traditional domes. However，the highly aspheric surface may introduce serious aberration which changes with the field of regard，and the fixed corrector can be used to correct these higher aberrations in the big field. This paper analysis the performance of the conformal dome and proposes a way for the optical corrector design by adding diffractive element into the fixed corrector. The simulation proves it's an effective way to improve the imaging quality of the conformal dome.