HfO2/SiO2, Y2O3/SiO2 ultraviolet multilayer thin films were annealed in air at 400 ℃ through different models: temperature rising linearly or step by step. It was found that the peak reflectances of all samples raised at 190～300 nm if the temperature was rised step by step. Corresponding single-layer thin films were annealed through the two different ways, the physical thickness of HfO2 layer reduced. If the temperature rised linearly, the refractive index of Y2O3 film reduced, which also resulting in blues shifting. If the temperature rised step by step, the wavelength would shift to shorter way because of the reduce of physical thickness. Microstructures of the films before and after annealing were characterized by X-ray diffraction (XRD) , it showed that annealing could crystallized the materials.If the temperature rising linearly, bigger crystals would cause more scattering, then reduce the reflectance of the film.