Abstract: The basic character at the interfaces of the positive and negative media is studied. The reflection coefficient and refraction coefficient are also given; the analysis shows the versatility of the principle of least action, Snell＇s law and Fresnell＇s law in the research on the left-handed material, and the negative refraction effect is explained.

Key words: negative refractive index, left-handed material, reflection coefficient, refraction coefficient, principle of least action