Abstract: The difference between the evanescent wave penetrating the lens made by the negative refractive material and the lens made by the refractive medium is analyzed. It realizes the phase adjustment, thus realizes wave focusing. Moreover, that the negative refraction material also amplifies evanescent wave oscillation amplitude is analyzed by using the principle of superposition （interference method） and the field quantity match law. The gain of negative refractive index medium for evanescent wave is obtained. The traveling wave and the evanescent wave all could focus the image formation. And it proposes that the evanescent wave penetrates the negative refractive material slab is equivalent to forming a LC oscillating circuit in the transmission line theory, and realizes the amplitude gain to the evanescent wave.

Key words: evanescent wave, negative refraction materials, focusing, amplitude gain