The light intensity distribution near the fiber probe of the Transmission Scanning Near Field Optical Microscopy(SNOM) was calculated by the model of R.D.Grober.The resolution,transmission depth and transmittance of the light intensity were discussed.The imaging process of excited biological fluorescent molecules was simulated,and it was found that the dipole direction of fluorescent molecules and he polarization of incident light influenced the detected signals.Both the pol arization direction of incident light and the dipole direction of fluorescent mo lecules would affect the fluorescent molecules imaging.