Sequentially deposited by thin film synthesis consisted of multilayer precursor film deposition and thermal treatment. It is especially useful in complex-ingredient or precise stoichoimetric controlling thin film synthesis. Gadolinium aluminate,a new good candidate system for many luminescence usages other than laser crystals,scintillation crystals,phosphors,contains many phases,such as Gd4Al2O9(GAM) ,GdAlO3(GAP) ,Gd3Al5O12(GAG) ,so precise stoichoimetry of the amorphous ingredient layers is very important to the final single phase film synthesis. In our work,Gd2O3 and Al amorphous layers(ingredients for gadolinium aluminate film) were deposited in a certain sequence on MgO(100) and Si(100) substrate by IM100(an ion beam sputtering instrument) . The multi-amorphous-layered precursor was annealed with two-step thermal treatment(diffusion at a low temperature and then crystallization at a high temperature) . The XRD(X-ray diffraction pattern) ,SEM(scanning electron microscope second electron image) and AES(Auger electron spectroscopy depth profiles) analyses were used to detect the film microstructures and properties. The analyses results showed that ion beam sputtering deposition could control ingredient stoichoimetric ratio by an in site depositing thickness measurement. During the two-step thermal treatment,diffusion at a low temperature would cost a rather long time to make the amorphous precursor film uniform(more than 120 h) ,and the suitable diffusion temperature should be around 400 oC. The crystallization temperature should be decided by the gadolinium aluminate phase types and cost rather less time(about 4 h) . The stable phases GAP and GAM should be annealed at 1300 oC or higher temperatures,but the metastable phase GAG should just be annealed at around 1100 °C. Sequentially deposited by thin film synthesis consisted of multilayer precursor film deposition and thermal treatment. It is especially useful in complex-ingredient or precise stoichoimetric controlling thin film synthesis. Gadolinium aluminate, a new good candidate system for many luminescence usages other than laser crystals, scintillation such as Gd4Al2O9 (GAM), GdAlO3 (GAP), Gd3Al5O12 (GAG), so precise stoichoimetry of the amorphous ingredient layers is very important to the final single phase film synthesis. In our work, Gd2O3 and Al amorphous layers (ingredients for gadolinium aluminate films) were deposited in a certain sequence on MgO (100) and Si (100) substrates by IM100 (an ion beam sputtering instrument). The multi-amorphous-layered precursor was annealed with two- step thermal treatment (diffusion at a low temperature and then crystallization at a high temperature). The XRD (X-ray diffraction pattern), SEM (scanning electron microscope second elec tron image) and AES (Auger electron spectroscopy depth profiles) analyses were used to detect the film microstructures and properties. During the deposition of controllable stoichimetric ratios by an in site depositing thickness measurement. During the two-step thermal treatment, diffusion at a low temperature would cost a rather long time to make the amorphous precursor film uniform (more than 120 h), and the suitable diffusion temperature should be around 400 oC. The crystallization temperature should be decided by the gadolinium aluminate phase The stable phases GAP and GAM should be annealed at 1300 oC or higher temperatures, but the metastable phase GAG ​​should just be annealed at around 1100 ° C.