By using the first-principles ultra-soft pseudo-potential (USP) approach of the plane-wave based upon density functional theory (DFT), the energy band structure, electron density of states, difference in charge density and optical properties of the intrinsic β-Ga2O3 and Si-doped β-Ga2O3 were calculated under generalized gradient approximation (GGA). The intrinsic β-Ga2O3 and Si-doped β-Ga2O3 films were deposited on sapphire (0001) substrates by pulsed laser deposition (PLD), the optical absorption spectra and reflectance spectra were measured. The results showed that the whole energy band moved to the low energy side, the conductivity was n-type, the optical band gap increased, the absorption edge shifted to short wavelength, and the reflectivity decreased. The calculation results are consistent with experimental data.