To convert Gaussian spot into flat line spot, a spheric-aspheric cylindrical lens is designed. The design is accomplished by using Zemax programming language to set operands and default optimization function. The design is compared with the aspheric lens-cylindrical lens group with the same performance parameters. The influence of the distance from the last surface to the image surface of the spherical-aspherical cylindrical lens on the length-width ratio of the linear spot and the flatness of the line-focused is analyzed. Compared with the aspheric lens-cylindrical lens group, the line spot size is the same but the flatness is normal (about 10% decline at the edge). Adjusting the distance from the last surface to the image surface in a certain range can make the flatness better (can reach 90%), but the aspect ratio is reduced (from 88.33 to 20.38). The results show that, in order to obtain the line spot with uniform distribution of energy, in the adjustable range of length-width ratio, the design of spheric-aspheric cylindrical lens can simplify the structure of beam shaping system and meet the requirements of lightweight. It is a feasible method.