In order to generate high-quality optical vortices, this paper presents theoretical analysis, improved design and experimental demonstration of a novel approach for optical vortex generation based on Sagnac interferometer. The additional phase difference π is introduced, based on analyzing the influence of the interference loop on the shear amount, a optical vortex generation setup on the basis of a Sagnac interferometer is built, then the related considerations are given and optical vortices of topological charge +1 and －1 are generated respectively. The intensity distribution and interference patterns at various propagation distance are experimentally recorded and analyzed with topological charge keeping +1 and －1. The improved setup can generate optical vortices with higher quality.