In this study, Sn-doped Ga₂O₃ thin films are prepared on sapphire substrate by radio frequency magnetron sputtering at ambient temperature, and then annealed at different temperatures (400–800 ℃) in nitrogen atmosphere. The corresponding metal-semiconductor-metal (MSM) solar blind photodetectors (PDs) are prepared based on those films before and after annealing to explore the influence of annealing temperature on the characteristics of the films and device properties. The results show that the as-deposited Sn-doped Ga₂O₃ film displays amorphous structure. With the increase of annealing temperature, the proportion of O_L, Ga³⁺ and Sn⁴⁺ ions in the film increase, and the band gap of the film decreases slightly, indicating that the conductivity of the film is enhanced and the quality of the film is improved. When the annealing temperature increases to 700 ℃, the β-Ga₂O₃ (${\bar 402} $) crystal surface diffraction peak appeares, indicating that the film begins to crystallize. As the annealing temperature increases to 800 ℃, the proportion of O_L, Ga³⁺ and Sn⁴⁺ 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 annealing temperature increasing, which is consistent with the changing trend of film characteristics. Then, based on Sn-doped Ga₂O₃ thin films before and after annealing, the MSM solar blind PDs are prepared to explore the influence 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 Ga₂O₃ solar blind PD. The optimal device performance can be obtained when the annealing temperature is 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 Ga₂O₃ films and the performance of solar blind PDs, which has certain guiding significance for the preparation of high-quality Sn-doped Ga₂O₃ films and high-performance solar blind PDs.