The extra-cavity quasi-continue spiral phase modulation method for generating high peak power quasi- radially polarized beam was studied, which show that the generated beam is not perfect radially polarized, the radially polarized components determine the longitudinal electric field distribution, and the transversal field distribution is determined by both of the radially and the azimuthally polarized components. Considering the Richard-Wolf vector diffraction theory, the spatial and temporal distribution of the electric field vectors around the focal spot for various purities were simulated. The results show that the spatial and temporal distribution possesses the features of centrosymmetry and oscillation attenuation, and will be remarkably affected by the carrier envelope phase. Furthermore, the analysis indicates that the interactions between the focused pulse and the electron will be significantly determined by the spatial and temporalvector distribution at the focal spot. The results will provide valuable basis for the laser-particler interaction analysis and further polarization convertor designs.