On the basis of Fresnel diffraction theory, surface microstructure of diffractive optical element (DOE) based on sphere using for aspheric surface was presented in this paper according to the same performance of introducing aspericity into optical system. Spherical DOE uses sphere taking the main focusing power and diffractive microstructure compensating the phase difference from aspheric surface to reference sphere. Thus, spherical DOE has the advantage of avoiding the difficulties of fabrication and measurement of aspheric surface and constructing the DOE microstructure in larger range than the DOE based on planar surface with the limitation of the critical dimension. An important aspect of this method is how to obtain the best fitting reference sphere to aspheric surface. The reference wavelength and the critical dimension were introduced into the limiting condition as the choosing criterion of the best fitting reference sphere. With this method all the lens surface of optical systems can be fabricated as sphere. The theory and method was proved and emulated with computer. Microstructure DOE based on sphere as substitution for aspheric surface is feasible in practice.