Based on the dipole-self-consistent field theory the influence of polarization of the incident light on the imaging quality of reflection mode SNOM is simulately calculated such as the system resolution and the image quality, and the theoretical explanation is given. The analysis result shows that the imaging quality greatly depends on the polarization of incident light at the probe tip of the microscope. In the near field imaging, the system resolution is better when the incident light is polarized vertically to the surface (via z-axis polarized) than that when it is horizontally polarized. When the incident light is x-axis polarized, the imaging achieved by scanning the object can reverse locally in contrast.