Abstract: With rigorous vector diffraction theory，the light intensity distribution of near-field diffraction for planar light waves with vertical incidence diffracted at small circular aperture is studied，and the spatial distribution characteristics of the diffraction light intensity simulation is calculated by computer.The Mablab simulation results show that the near-field diffraction belongs to Fresnel diffraction，and similar to Fraunhofer diffraction.

Key words: small circular aperture, vector diffraction theory, near-field diffraction