The invention discloses a sub-arc-second large-aperture compact optical structure for detecting dim point targets. The sub-arc-second large-aperture compact optical structure comprises a lens drum, as well as an optical system and an image surface which are arranged inside the lens drum, wherein the optical system comprises a first aperture correcting lens, a secondary reflector, a second aperture correcting lens, a first view field correcting lens, a second view field correcting lens and a main reflector; the axle centers of the first aperture correcting lens, the secondary reflector, the second aperture correcting lens, the first view field correcting lens, the second view field correcting lens and the main reflector are sequentially arranged in the same straight line; the secondary reflector is clung to the side surface of the first aperture correcting lens; the coverage range of the side surface of the first aperture correcting lens of the secondary reflector meets the imaging requirement; a circular hole is formed in the center of the main reflecting lens; the first view field correcting lens and the second view field correcting lens are arranged in the range limited by an opening of the circular hole; the image surface is arranged at the center of the side surface of the main reflector. The measurement accuracy of the sub-arc-second large-aperture compact optical structure is superior to the sub-arc-second grade; the optical aperture is equivalent to the total optical length; the structure is compact in structure and is suitable for detection of the dim point targets such as super-high-accuracy star sensors and space fragments.