Abstract: According to the Fresnel-Kirchhoff diffraction integral formula, numerical calculation methods for the circular aperture diffraction irradiated by a point source or a plane light or a Gauss beam are given. The analytic calculation formula for these three kinds of circular aperture Fresnel diffraction and their special circumstance Fraunhofer diffraction are deduced with correlation methods, and their paraxial zone diffraction fields are simulated with Matlab software. The simulations show that these two calculation methods for the three kinds of common and important circular aperture diffraction are effective and feasible.