Abstract: Based on the aperture field theory, near-field radiation behaviors of super-Gaussian circular aperture antenna are discussed, and the near-field gain expression at focusing point while focusing is obtained. Corresponding simulations are conducted by selecting different observing points of antenna. The results show that the radiation patterns keep invariant in spite of the ratio of aperture radius to beam waist(RAW), when the distance between the observing point and antenna is less than 0.3 times the focal length, and the super-Gaussian order is greater than 4. Once the observing point lies on the focus, for given RAW, the radiation patterns vary with the super-Gaussian order. However, when the RAW is over 4, the radiation patterns keep stable and no sidelobes exist for high-order beams.