After introducing the characterastics of FC(n) and LiNbO3 superlattice systems con- structed following FC(n), we analytically obtained the formulae of the output power of the second-harmonic-generation light and the efficiency of the output power versus input power by means of the small-signal approximation. The relationship between the output power per unit area of the second-harmonic-generation light of ordinary-light s(2ω)0 and the wavelenght of the fundamental beam was given. It was found that there exist four harmonic spectral lines with high transforming efficiency in visible light zone. The similar result was also got but the number of the lines is six. In this paper two kinds of interesting vacancy effect were discussed.