A continual zoom system, which can be used as the fore objective of the developed hyperspectral imager, is designed, according to the specification and application requirements of the imager. The lens have the advantages of high speed, visible light wavelength range, long effective focal length (EFL) high etendue and imagery telecentricity. The structural selection and the initial parameter calculation are introduced in detail. The designed zoom optical system with mechanical compensation is presented. The zoom ratio is 4×, and the relative aperture is 1∶2. The effective focal lengths are 55 mm and 220 mm respectively at short and long focus end, and the corresponding field of view angles from 2° to 8°. The distortion is lower than 0.6%. The modulation transfer function (MTF) value at the spatial frequency of 66 lp/mm is higher than 0.5. The designed zoom system can meet the application requirements of the hyperspectral imager.