Design method of traditional diffractive optical element (DOE) is only applicable to a single wavelength. But multiple DOEs are often required in the holographic projection display and color image generation, which is more complicated to greatly limit the application scope. A novel design method of DOE used for multi-wavelength simultaneity is present. The Gerchberg-Saxton (GS) algorithm is adopted to design individual DOE at every wavelength. And then individual DOE structure at the longest wavelength is regarded as the iterative side, in every pixel of which the integral 2π phase height is added. Structure compare the equivalent phase of the corresponding pixel with that of the individual structure at the other wavelengths. When squared distance is the least, the iteration is complete. This method is simulated and the parameters are analyzed by using Matlab. DOE structure is quantized to the 16- level, which validates the feasibility of this method in actual production.