Using Radio Frequency Magnetron Sputtering (RFMS) equipment, gallium oxide (Ga2O3) films were deposited on sapphire substrates. Then the samples were annealed at 700 °C, 900 °C, and 1100 °C for 120 min in the air atmosphere to convert them into β-Ga2O3 films with different crystalline quality. The effects of annealing temperature on the properties of β-Ga2O3 thin films were investigated. The crystal structure and surface morphology were tested by X-ray Diffraction (XRD), absorption spectroscopy, and Atomic Force Microscopy (AFM). The results obtained show that, within a certain range, as the annealing temperature increases, the intensity of the XRD peaks increases, the Full Width at Half Maximum (FWHW) – decreases. The crystal grains “engorge” as the temperature rises, and the degree of crystallinity of the samples becomes better.