Abstract: To study the influence of substrate temperature on the refractive index of alumina thin film and the film thickness, we accomplished Al2O3 thin films by ionassisted electron beam evaporation method under different substrate temperatures and the same Tooling factors. Based on the related theory of optical film, using the spectrophotometer to measure the spectral transmittance, we calculated the actual film thickness which were 275.611 nm~348.447 nm and the refractive index under 25℃~300℃. With the curves by numerical calculation and the experimental results by simulation, the effect of substrate temperature on refractive index of thin films and deposition efficiency was given.