In order to design an optical system with focal length range from 17 to 1 700 mm, a proper initial optical layout is selected first, the rule of system performance influenced by Guassian solution is found through comparing Guassian optical calculation results, and the key parameters of the system are selected. Then the configuration of each assembly is chosen through analyzing the relative aperture and characteristics of aberrations, and the system aberration is corrected and balanced. The total track of the result lens is 760 mm, the modulation transfer functions at 50 lp/mm for each zoom configurations and all fields of view are greater than 0.3, and all indexes satisfy the command of system.