A design method of diffractive optical elements (DOE) based on dual-lens system is proposed. In the dual-lens system,the transmission and focusing of the beam need to be expressed by twice Fresnel diffraction,in order to accelerate the computing speed,we converted the Fresnel formula to the form of which contains fast Fourier transform so that the traditional iterative algorithm can meet the different design environments. By using this design method,we get the diffraction efficiency more than 90% in theory,and processes the element and make the experimental test,the effect of beam shaping that we expected is achieved. It is worthwhile,for more complex system of DOE design there,and there may be potential function for the high-power laser systems.