Application value of the Gaussian beam with flat-top shaping and some main shaping methods were introduced. Because of the advantages of aspherics, aspherics shaping method was studied, Fermi Dirac function was chosen as a flat-top beam distribution model, and the relationship between its flat-top distribution and the characteristic parameters was analyzed. By analyzing aspherics shaping principle theoretically, according to the law of conservation of energy and ray tracing function, aspheric surface form expression was deduced. Considering the processing factors, the effects of system parameters on the spherical degree was analyzed. And then, by choosing appropriate parameters, MATLAB software was used to solve numerical solution of mapping relation and surface shape curve and fit to get aspheric coefficient. By using ZEMAX optical software to make system modeling, the output beam of light intensity distribution and propagation characteristic could be gotten through the physical optics propagate-POP simulation. As a result, output beam of the flat-top quality is close to the expected effect, and its error mainly comes from numerical calculation accuracy and edge diffraction.