Abstract: A design of sunlight fiber coupling system with long focal length and large aperture was introduced. In order to reduce the spherical aberration and chromatic aberration of the large aperture single-lens during converging sunlight, a method of reducing aberrations optical system added at the back of focusing lens was proposed, and the optical system that was applicable for optical fiber coupling system was designed and optimized by using Zemax software. The radius of spot size was 45.043 m, energy concentration was more than 95%, aperture angle was 9.090 2, and the total length of system was 525.584 mm. The coupling requirements of quartz optical fiber with numerical aperture of 0.22 and core diameter of 1.5 mm were satisfied.