Based on Maxwell equations, we have discussed the different evanescent fields made by excitation with different polarized incident fields, and their influence on fluorescence emission. Our analysis showed that the incident light of p-polar ization produces an ellipitically polarized evanescent field; at the same time, the incident light of s-polarization produces a pure s-polarization evanescent f ield. The probability of the excitation of fluorescent molecules by an evanescen t wave varies with the fluorescent molecules orientation, which will in turn res ult in the anisotropic fluorescence emission.