Abstract: In the case of parallel plane wave approximation，the Fresnel-Kirchhoff diffraction

integral formula is solved numerically，and the light intensity distribution diagram of the

diffraction through the circular aperture is obtained. Through the numerical analysis of the

longitudinal and transverse light intensity distribution diagrams，it is

concluded that the intensity of the light on the axis is determined by the Fresnel number. When the

Fresnel number is greater than 1，it is the Fresnel diffraction zone，and when the Fresnel number is less than 1，it

is the Fraunhofer diffraction zone. In the near field，the intensity of the light distribution is a

ring-shaped stripe of bright and dark; in the far field，the beam evolves into a Gaussian beam with

a waist at the circular hole. The simulation results are

basically consistent with the theoretical and experimental results. The light diffraction theory is

visualized intuitively with the simulation results.

Key words: numerical method, circular aperture diffraction, Fresnel number, Gaussian beam