In this paper, a CO2 laser (λ1=9.3 μm and λ2=10.6 μm) beam expanding system with high variable expanding ratio is presented. The system lens is designed as a combination of four singlet lenses fabricated with chalcogenide glass material Ge20Sb15Se65, the advantage of the superior property of chalcogenide glasses is molding preparation of surfaces. The laser beam expander is designed as start point of two component zoom design idea, with the specific wavelength, incident diameter, material and other optical parameters on the basic parameters of the ideal target optical system. By using Zemax optical design software, the optical structural parameters of the system are optimized. This optical design of CO2 laser beam expanding system with high variable expanding ratio is good beam collimation, simple structure and also has low cost. The results show that this optical system has a maximum diameter of the incident beam is 6 mm, the bandwidth is 100 nm, variable beam expanding ratio is between 2 to 7 and the maximum wavefront aberration is less than 1/4 of central wavelength. Thus, it can be applied in all kinds of opto-electrical fields.