Abstract: The principle of coronagraph requires that stray light in coronagraph system must be kept at an extremely low level. Based on the principle of mirror coronagraph, the internally occulted mirror coronagraph is designed by analyzing its optical character and the basic rules of suppressing the stay light. In this system, the FOV is 0.67degree, the aperture is 47mm, the focal length is 768mm, the total length is 1200mm, the MTF value at 30lp/mm is above 0.6, the radius of spot is less than 2.5 um,and the image quality of the system approaches the diffraction limit.Considering the character of stray light in system,the structure of suppressing stray light is built.In the system,the main sources of stray light can be suppressed entirely .The system can achieve a level of 10-6-10-8B⊙ approximately in suppressing stray light,and so it can get high quality coronal images.