Cubesat has the advantages of low launch cost， short cycle， small size， and low power requirement. It is highly suitable for the first verification of certain innovative technologies， satellite-borne integrations， or distributed space networks to provide remote sensing and communication services， such as constellations and flight formations. Herein， an optical camera system suitable for 3U cubic star platforms is designed. First， based on a comparison and analysis of different optical system structures， the proposed system uses a coaxial reflex structure. The focal length， field of view angle， and working waveband of the system are 460 mm， 4°， and 450-700 nm， respectively. Then， by analyzing the transfer function of the system， the corresponding relation between the system aperture and blocking ratio is obtained. The aperture and F number are determined to be 92 mm and 5， respectively. Finally， the system is optimized. The system uses the cassette system as the prototype， and the primary and secondary mirrors are Mankin mirrors. After optimization， the image quality of each field of view is close to the diffraction limit and the transfer function at the Nyquist frequency is greater than 0.3.