The ideal perfect vortex beam is a special beam whose intensity distribution does not change with the change of the topological charge. Compared with ordinary vortex beam, it can greatly improve the application efficiency in particle manipulation and optical fiber transmission. In order to explore the free space propagation characteristics of the perfect vortex beam, this article uses Hank transformation to calculate and analyze the effects of the topological charge, the initial surface ring radius and the ring width on its diffraction characteristics in detail, it is found that the perfect vortex beam does not have the characteristic of non-diffraction, and the halo will broaden with the increase of the diffraction distance and gradually transform to the Bessel function. When the radius of the initial surface increases or the width of the ring decreases, the diffraction effect increases, and the effect of the ring width is greater than the ring radius. Compared with the previous two cases, the topological charge has less influence on the diffraction effect. The research in this paper is expected to provide a useful theoretical reference for the further application of the perfect vortex beam.