A new structure is adopted to design a visible and near infrared large aperture telescope with 1.2 m diameter, 2-6 m focal length, and 1/1.67-1/5 relative aperture. For meeting the requirement of modern ground-base large telescope, the front primary system using Cassegrain reflective form. And the back part uses three group mechanical compensation zoom refractive system, which makes the structure more simple and compact. Based on Gauss optics calculation and analysis of aberration, the initial form of each group was determined, and the whole system was optimized subsequently. The design results show that all of the optical indexes satisfy the command of the system, and the structure was compact, the compensation curve was smooth. The design demonstrates that the form is an effective optical structure for large aperture continuous zoom telescope.