A new lens designed for the long focal length, catadioptric zoom telescope is presented. By setting the variable diaphragm near the primary mirror, there is no necessity to use a floating variable diaphragm in the zoom part. Then using the re-imaging form and field lens, the zoom part only contains variator and compensator, without focus unit and primelens as usual and there is no unusual partial dispersion glass used for the correction of secondary spectrum, so the complexity of zoom part is greatly reduced. By using this new lens form, a catadioptric zoom telescope working in the visible wavelength band with variable focal length between 600 and 3000 mm, 300 mm maximum aperture is designed and then optimized. The modulation transfer function (MTF) of this optimized lens is greater than 0.3 at 60 lp/mm across all the focal lengths and field of view. The result indicates that this lens reaches good image quality and is cost-effective for manufacture, so this new lens is very suitable for the long focal length, visible zoom imaging system.