The invention relates to a La-CeO2 doped transition layer film and a preparation method thereof, belonging to the technical field of high-temperature superconducting material preparation. The La-CeO2 doped transition layer film contains a Ce(1-x)LaxO2 composite oxide solid solution, wherein x is larger than or equal to 0.1 but small than or equal to 0.3; and the thickness of the transition layer film is 30-250 nm. The invention takes organic cerium salt as precursor salt and lanthanum acetylacetone as a lanthanum source, adopts a chemical solution method to prepare a precursor solution, then coats the precursor solution on a metal base band by a spin coating method or a dip coating method and then preparer the La and CeO2 mixing transition layer film by a heat processing technology. The invention has low preparation cost and precise and adjustable lattice constant of a Ce (1-x) LaxO2 transition layer film, can realize the integration of multiple transition layer functions, decrease the prior complex transition layer structure, and the like.