Abstract: Eu³⁺ doped β-Ga₂O₃ phosphor was synthesized via hydrothermal method. The effects of thermal annealing temperature on the optical properties of Eu³⁺ doped β-Ga₂O₃ phosphor were studied. X-ray diffraction method was used to identify the phase and crystal growth orientation of the phosphor sample. The results show that the Eu³⁺ introduce into β-Ga₂O₃ lattice with the diffraction peak position of the sample shifts to a different angle. Raman spectrometer was used to detect the material structure and configuration of the sample. The Raman peak of the sample is consistent with the Raman peak of β-Ga₂O₃ structure, and reach at the maximum peak at 800 ℃, indicating that the crystallinity of the sample is the best temperature. Surface morphology of the phosphor sample were measured and observed using a scanning electron microscope. The results show that the properties of high uniformity and good crystallinity in different thermal annealing temperature. Under 395 nm excitation, it can be seen that 591 nm orange light emission peak attributes to Eu³⁺(⁵D₀→⁷F₁) and 612 nm red light emission peak produced by the Eu³⁺(⁵D₀→⁷F₂) transition, mainly red light emission peak. With the increase of thermal annealing temperature, the phosphor sample luminescence intensity increased first and then decreased, indicating that the phosphor sample have the higher luminescence intensity at 800 ℃. The results of powders were synthesized by hydrothermal method showed that the properties of high purity. The thermal annealing process is simple and low cost, which can effectively deal with the crystallinity of the sample. By reducing the defects in the material through the stress action, the crystallinity is higher and the luminescent properties of phosphors are improved.