We calculated the band structure and density of states of fluorite type TiO2 using density functional theory. The results show that fluorite type TiO2 is an indirect-band-gap semiconductor, and its indirect band gap Eg=2.07eV is smaller than that of rutile or anatase TiO2. To make optical properties clear, we calculated the complex dielectric constant of fluorite-structured TiO2 and compared it with the rutile TiO2. The results illustrate that the fluorite TiO2 has a large static dielectric constant of 8.31, and ε1xy(0)=6.01 and ε1z(0)=7.07 for rutile TiO2 show excellent agreement with experimental data. Also, two new absorption peaks located at 51nm and 153nm respectively were observed and the absorption range of fluorite TiO2 extends to the visible region.