Exactlv measurement of the fluctuation of the atmosphere refractivity is important for the research on the optical property of atmosphere an and it＇s application on the environmental detection. A theoretical model of measuring the fluctuation of the atmosphere refractivity using the near-field optical method is proposed： The surface plasmon resonance effect of the metal is stimulated by the internal total reflection. As a result the propagation mode will be induced in the planar waveguide. The point of the maximum slope in the curve of attenuated internal total reflection is selected as the angular of the incident beam. The variation of the intensity of the reflection beam demonstrates the variation of the refractivity of the atmosphere. The precision achieved using the numerical simulation is 0.000005.