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The effect of La doping on the electronic structure and optical properties of SrZiO3 and Sr2TiO4 is investi-gated by the first-principles calculation of plane wave ultrasoft pseudopotential based on the density function theory (DFT). The calculated results reveal that the electron doping in the case of Sr0.875La0.125 TiO3 and Sr1.875La0.125 TiO4 can be described within the rigid band model. The La3+ ions fully acts as electron donors in Sr0.875La0.125 TiO3 and Sr1.875La0.125 TiO4 systems and the Fermi level shifts further into the conduction bands (CBs) for Sr1.875La0.125 TiO4 compared to Sr1.875La0.125 TiO3. The two systems exhibit n-type degenerate semi-conductor features. At the same time, the density of states (DOS) of the two systems shift towards low energies and the optical band gaps are broadened. The Sr1.875La0.125 TiO4 is highly transparent with the transmittance about 90% in the visible range, which is larger than that of Sr1.875La0.125 TiO3(85%). The wide band gap, small transition probability and weak absorption due to the low partial density of states (PDOS) of impurity in the Fermi level result in the optical transparency of the films.