The electronic structure,dielectric function,complex reflectivity index，complex conductivity and absorption spectra of the perfect BaTiO3 crystal were calculation using CASTEP codes.The calculation results indicate that the imaginary parts of dielectric function,complex reflectivity index，complex conductivity and absorption spectra of the crystal are related to the electronic structure of the crystal.The calculation results are in good agreement with the experimental results.The results will be helpful to give an insight into the essentiality of optical properties of the material and will provide the basis to further study the properties of the crystal with defects.