Abstract: The linearly polarized phase vortex beam has a unique spiral phase distribution and central singularity. The topological charge of the vortex beam can be integral and fractional. The integral vortex beam has a ring light intensity distribution with dark spots in the center, while the fractional vortex beam has a unique radial gap, which belongs to the non-rotational symmetric beam and has astigmatic characteristics. In this paper, the astigmatism coefficient is proposed to characterize the astigmatism characteristics of vortex beam. A linearly polarized phase vortex beam is generated by using a spiral phase plate. Its beam quality and astigmatism characteristics are measured. The propagation characteristics and beam quality of vortex beam with different topological charge is numerically simulated, and the astigmatism coefficient changing with topological charge is analyzed. The results indicate that when the topological charge is integer, the beam has no astigmatism and the astigmatism coefficient is zero; when the topological charge is semi-odd, the astigmatism characteristic of the beam is obvious, and the astigmatism coefficient reaches the maximum; as the integral part of topological charge increased, the maximum value of astigmatism coefficient decreases.