Abstract: A focusing optical system used for calibration of ultraviolet and visible light optical axis parallelism was designed with the focusing range of 70 m~. Aiming at most calibration systems- problems that can not focus at present, a method was put forward, which can calibrate the ultraviolet and visible light optical axis parallelism, and focus the ultraviolet part. We used the off-axis Cassegrain system as the initial structure to design, and added the focus group and compensation group into the traditional Cassegrain system so as to implement the focusing and aberration compensation. The designed system can effectively solve the calibration problems of the ultraviolet and visible light double-axis parallelism and improve the calibration efficiency. Also, the modulation transfer function (MTF) values and spot diagram both close to the diffraction limit under different object distances, moreover, the energy concentration reaches 90%, the view image quality of the entire field is even and image surface is clear, which are good for the follow-up image processing.