Based on vectorial Debye integral,the light field and intensity distribution expressions are presented when partially polarized Gaussian beams pass through a high numerical-aperture objective. Numerical calculations are taken to analyze the tightly focusing properties of partially polarized Gaussian beams with various degrees of polarization. The research results show that the total intensity distribution and each direction components of partially polarized Gaussian beams on the focal plane will change with the change of polarization. It is also found that the values of the maximal angle of the high numerical-aperture objective will influence the total intensity on the focal plane. Therefore,the intensity distribution of partially polarized Gaussian beam on the focal plane can be controlled by adjusting the polarization and the maximal angle of the high numerical-aperture objective.