In order to solve the problem of poor plate-making quality caused by distortion and field curvature of the plate-making lens of the external drum thermal computer to plate (CTP)equipment, a low-distortion and low-field-curvature plate-making lens optical system was designed using ZEMAX software. Tolerance analysis and experimental verification have been carried out. The results show that the optical system is consisted of six lenses, the working wavelength is 830 nm, the field curvature is less than 1 μm, the distortion is less than 0.1%, and the modulation transfer function is greater than 0.7 at the full field of view of 200 lp/mm. All the lenses in this system are designed with a standard spherical surface, and the plate-making effect is good, which can meet the actual plate-making production needs, and has a certain market prospect.