We have recently shown that spiral phase plates (SPPs) with continuous surface can be fabricated with one time exposing process only . Four categories of SPPs with different topological charges at wavelength of 532 nm were prepared, and the corresponding vortex beams were obtained. In this paper, in order to verify the optical effects' quality of the SPPs, the optical characteristics, including the diffractive and interferential characteristics, were systematically analyzed in the Fresnel diffraction region. In addition, the optical characteristics have been used to describe the surface profile of the SPPs. The results show that the SPPs have good surface quality and excellent optical effects. Compared with the other generation methods for vortex beam, this method is particularly suitable for obtaining a vortex beam with high efficiency and continuous phase and is extremely promoting R&D of the corresponding applications.