In this study, Sn-doped Ga ₂O ₃thin films were prepared on sapphire substrate by RF magnetron sputtering at room temperature, and then annealed at different temperatures (400-800℃) under nitrogen atmosphere. The corresponding MSM solar blind photodetectors (PDs) were prepared based on those films before and after annealing to explore the effect of annealing temperature on the characteristics of the films and device properties. The results show that the as-deposited Sn-doped Ga ₂O ₃film displays amorphous structure. With the increase of annealing temperature, the proportion of O _L, Ga ³⁺and Sn ⁴⁺ions in the films increases, and the band gap of the films decreases slightly, which indicates that the enhanced conductivity of the films and improved film quality. When the annealing temperature increased to 700℃, the β-Ga ₂O ₃(−402) crystal surface diffraction peak appeared, indicating that the film began to crystallize. As the annealing temperature increases to 800℃, the proportion of O _L, Ga ³⁺and Sn ⁴⁺decreases, and the quality and conductive properties of the film deteriorate, which may be attributed to Sn surface segregation and Al diffusion into the film from the substrate. In addition, the average particle size and surface roughness of the film surface increase with the increase of annealing temperature, which is consistent with the changing trend of film characteristics. Then, based on Sn-doped Ga ₂O ₃thin films before and after annealing, the MSM solar blind PDs were prepared to explore the effect of annealing temperature on device performance. The quality of the film and its conductive characteristics play a role in regulating the performance of Sn-doped Ga ₂O ₃solar blind PD. The optimal device performance could be obtained when the annealing temperature was 700℃ with a low dark current of 89.97 pA, a responsivity of 18.4 mA/W, a light-dark current up to 1264, and the rise/fall time of 0.93 s/0.87 s. In summary, the annealing temperature has an important effect on the characteristics of Sn-doped Ga ₂O ₃films and the performance of solar blind PDs, which has certain guiding significance for the preparation of high quality Sn-doped Ga ₂O ₃films and high performance solar blind PDs.