A method for preparing rare earth doped strontium cerate nanometer crystal thin film by organic polymer presoma method is disclosed. It is prepared by: preparing initial solution with cerous nitrate, strontium nitrate or strontium acetate, rare earth oxide as raw materials, determining the proportion by prepared thin film composition, the composition of thin film is SrCe1-xRExO3, the range of x volume is 0.02-0.20, concentration of initial solution is 0.1-0.4mol/L, taking ethylene as complexant, the adding account of ethylene is 2-6 times of metal ionic total account, mixing and supersonic oscillating, heating in water bath under 50-100deg.C, adjusting PH value, the system being heated reacting to produce organic polymer, film coating with 1500-3000rpm circulating speed on required chip by glue equalizer when viscosity reaching 100-300cP, infrared drying or vacuum drying, second film coating, drying until reaching the required thickness, and producing nanometer crystal thin film under 900deg.C reacting.