A real ray tracing method was used to simplify the optical design of a Gaussian beam shaping system. The principle of shaping Gaussian beam was studied theoretically and the Flattened Lorentzian(FL) function was chosen as the distribution expression of the flattened beam. The relationship of coordinate transformation of arbitrary rays in an incident plane and an image plane was deduced based on the law of energy conservation. Then, according to the characteristics of this system, Zemax Programming Language (ZPL) was used to compile ZPL macro orders to calculate the coordinate transformation, and the real ray tracing method was adopted to design the optical Gaussian beam shaping system. Finally, the aspheric lens system was processed by single point diamond turning techniques and its shaping ability was tested by the optical analyzing software. Testing results indicate that the system can achieve the conversion from the Gaussian beam to the flattened beam, and the uniformity of flattened beam is 87.1%. The method is not only simple but aslo practical and has a significant engineering application value.