The invention discloses a direct preparation method of a (Y1-xLnx)2(MoO4)3 thin film. The direct preparation method comprises the following steps: dissolving Y(NO3)3.6H2O or Y(NO3)3.6H2O and Ln(NO3)3.6H2O into de-ionized water to prepare a solution with the total rare earth ion concentration of 0.005mol/L to 1mol/L; adding EDTA (Ethylene Diamine Tetraacetic Acid) or citric acid, an NaOH solution, Na2MoO4.2H2O, KCl and HNO3 into the solution; after uniformly mixing, obtaining an electrolytic deposition solution; putting the electrolytic deposition solution into a water bath to enable the temperature of the electrolytic deposition solution to reach needed temperature; inserting a three-electrode system into the electrolytic deposition solution and depositing one layer of thin film on conducting glass through electrolytic deposition reaction; washing the thin film with de-ionized water and absolute ethyl alcohol respectively; then putting the thin film into an air blowing drying box and drying; putting the dried electro-deposited thin film into a tubular furnace and carrying out heat treatment to prepare the (Y1-xLnx)2(MoO4)3 thin film. The direct preparation method is simple to operate; compared with a traditional method of firstly preparing power and then forming the film, a thin film preparation method is extremely simplified; meanwhile, influences, caused by a powder shape, on the film forming quality, are avoided; the method provided by the invention is simple to operate, short in consumed time and good in thin film quality.