Abstract: The aberration characteristics of refractive optical system with large relative aperture and long focal length were analyzed. And a lens with 300 mm diameter, 540 mm focal length, 500 -850 nm operating wavelength range, and 2field of view was designed. First, as the secondary spectrum was the most prominent aberration, the Petzval form was chose as the initial configuration, and after complication, the configuration with three components with large air space was used, which was good for aberration correction and element size reduction. Then the partial dispersion and abbe number of typical glasses were recalculated and modified for the used wavelength, and P-V map is draw, then the glasses with some secondary spectrum correction ability and fine optical performance were chose. Finally the secondary spectrum of the system is reduced to 0.06 mm, which show that the system is apochromat. The design results demonstrate that the MTF of all field of view at Nyquist frequency 39 lp/mm is higher than 0.8, and 80% energy of the system encircled in 8um, which is less than a pixel size, and the distortion is less than 0.1%. All indexes satisfy the commands of system.