As a new kind of artificial materials, metamaterials have attracted wide attention, because they can present special properties which not exist naturally or hard be realized. Based on the quantized method of the LC circuit model, our group has studied the elementary excitation in metamaterial and introduced its “quasi-particle”. By using the two-photon inference, the quantum property of metamaterial and the correctness of the quantized method were proved. This quantized method was further used to investigate the interaction between metamaterial and active material, and the amplification by the stimulated emission radiation can be found in this system. These results show that metamaterials not only can steer the light in classical regime but also have a potential application in quantum optics.