Abstract: A varifocal method by using double-motor to control the zooming lens and the compensating lens instead of cam-curve muff was described, and a mechanical compensated zoom lens with focal length range of 342.76 mm~13.15 mm and relative aperture of 1/4 was also presented. The zooming lens was moved step-by-step and the compensating lens was moved following the zooming lens by position tracking method (CAMIMG), so that the lenses were positioned accurately in the whole zooming range. The pulse data corresponding to the positions relationship of zooming lens and compensating lens was stored in the CAM table according to optical design cam datum by digital serve control cam arithmetic, therefore the relationship of the two different movement velocity axes in each position was determined. The results show that the image is clear and steady in the whole varifocal range, the position resolution of zooming lens and compensating lens is 0.18 m, the optical axis consistency is about 1.9 in horizontal direction and 1.3 in vertical direction.