In this work, the formation energy, band structure, state density, differential charge density and optoelectronic properties of undoped β-Ga₂O₃ and Si doped β-Ga₂O₃ are calculated by using GGA+U method based on density functional theory. The results show that the Si-substituted tetrahedron Ga(1) is more easily synthesized experimentally, and the obtained β-Ga₂O₃ band gap and Ga-3d state peak are in good agreement with the experimental results, and the effective doping is more likely to be obtained under oxygen-poor conditions. After Si doping, the total energy band moves toward the low-energy end, and Fermi level enters the conduction band, showing n-type conductive characteristic. The Si-3s orbital electrons occupy the bottom of the conduction band, the degree of electronic occupancy is strengthened, and the conductivity is improved. The results from dielectric function ε₂(ω) show that with the increase of Si doping concentration, the ability to stimulate conductive electrons first increases and then decreases, which is in good agreement with the quantitative analysis results of conductivity. The optical band gap increases and the absorption band edge rises slowly with the increase of Si doping concentration. The results of absorption spectra show that Si-doped β-Ga₂O₃ has the ability to realize the strong deep ultraviolet photoelectric detection. The calculated results provide a theoretical reference for further implementing the experimental investigation and the optimization innovation of Si-doped β-Ga₂O₃ and relative device design.