(Pb, La)TiO3 (PLT) ferroelectric thin films are one of the promising candidates for applications in dynamic random memory and pyroelectric detectors, etc. However, the chemical composition in the surface layer of thin films is usually different from that in the “bulk” region of the thin films. For instance, it has been reported that there is Pb, Ti, or La enrichment in the surface layer of the (Pb, La)TiO3 thin films. According to a numerical modeling using effective-medium theory, which was developed in our group, we discussed the effect of the surface layer on the dielectric constant of (Pb, La)TiO3 thin films. The effect of Pb, Ti, or La enrichment in the surface layer on the dielectric constant of PLT thin films was discussed. And a case of the “upgraded” and the “down-graded” thin films was expatiated and discussed.