Based on the Galileo aspheric lens beam shaping system, a single aspheric lens beam shaping system for TEA CO2 lasers is designed. The optical design is based on geometrical optics, and the differen-tial equations expressing conservation are solved by using energy law and constant optical path length con-dition. By the Romberg numerical integrating algorithm and the method of the nonlinear least square, the sags of aspheric surfaces are obtained. The system’s performance is optimized using the optical design soft-ware ZEMAX, and the simulation result shows that the optical path difference(OPD) of the flat-top output is ±0.01 λ,the peak-valley wavefront error is 0.0002 λ,which proves it being collimated. The simpler sys-tem avoids the disadvantages of large volume and difficulty in adjustment of traditional Galileo system, and makes itself easy to process and adjust.