The electronic structure and optical properties of orthorhombic CaTiO<sub>3</sub> have been investigated using the first principle projector-augmented wave (PAW) pseudopotential method. Exchange–correlation effects are treated by the generalized gradient approximation (GGA). The band structure and density of states (DOS) show that orthorhombic CaTiO<sub>3</sub> has direct band gap of 2.43 eV at gamma point, and O-2p to Ti-3d states are predominant in the top of valence band and the bottom of conduction band. Furthermore, the optical properties form complex dielectric function has been presented. The static dielectric function and the peaks position distribution of imaginary part of complex dielectric function has been discussed, which shows the optical transitions based on the electronic structure. These results suggest orthorhombic CaTiO<sub>3</sub> may have special optical applications.