Abstract: Base on the theory of Mie light scattering,the intensity distribution of Whispering gallery modes(WGMs) in a spherical cavity is calculated.After inserting a spherical cavity into various liquid mediums,the ratios of evanescent field to the whole mode field(η) and the quality factor(Q) of WGMs are calculated.With a decrease of relative refraction index,the calculated results show that the Q value of a WGM is degraded,however,η value is increased.A high η value means a high coupling efficiency,which is benefit to the stimulated emission amplification of evanescent field coupled gain.