Defect formation energies,electronic structures and optical properties of Sn-doped β-Ga_2O_3,F-dopedβ-Ga_2O_3,and Sn/F co-doped β-Ga_2O_3 were calculated using the first-principles.The calculated results of the pure and Sn-doped β-Ga_2O_3 using the local-density approximation(LDA) method show that the lattice parameters and electronic structures are in agreement with previous data.The defect formation energies demonstrate that the doped systems are relatively easy to form under O-rich conditions.Sn-doping,F-doping and Sn/F co-doping makeβ-Ga_2O_3 become an n-type semiconductor.Sn/F co-doping β-Ga_2O_3 has the smallest effective electron mass and the biggest relative electron number,which is expected to possess good conductivity.Sn/F co-doping β-Ga_2O_3displays an intense absorption in visible light. Defect formation energies, electronic structures and optical properties of Sn-doped β-Ga 2 O 3, F-doped β-Ga 2 O 3, and Sn / F co-doped β-Ga 2 O 3 were calculated using the first- doped β-Ga 2 O 3 using the local-density approximation (LDA) method show that the lattice parameters and electronic structures are in agreement with previous data. The defect formation energies demonstrate that the doped systems are relatively easy to form under O-rich conditions.Sn -doping, F-doping and Sn / F co-doping makeβ-Ga 2 O 3 become an n-type semiconductor. Sn / F co-doping β-Ga 2 O 3 has the smallest effective electron mass and the biggest relative electron number, which is expected to possess good conductivity. Sn / F co-doping β-Ga_2O_3displays an intense absorption in visible light.