The electronic structure, dielectric function, complex reflectivity index and absorption spectra of the perfect PbWO_4 crystal have been calculated using full-potential (linearized) augmented plane-wave ((L)APW) + local orbitals (lo) method.The peaks of the absorption spectra corresponding with electronic transition have been studied. The calculated results indicate that the dielectric function, complex reflectivity index and absorption spectra of the crystal are related to the electronic structures of the crystal. Since the perfect PWO crystals do not occur absorption spectra in the visible region, the perfect PWO crystals are transparent crystals.