Phase transition of TiO₂ from rutile to fluorite is investigated with first principles plane-wave pseudopotential density functional theory,together with a quasi-harmonic Debye model.The rutile-to-fluorite(R-F) transition pressure and temperature obtained are 45.32 GPa and 2029 K,respectively,which are consistent with experimental and calculated results.The R-F transition pressure increase with increasing temperature.By fitting,we estimate transition pressure at experiment temperatures(T=1900-2 100 K,P_t=47.604-47.756 GPa).Moreover,dependences of relative volume V/V₀ on pressure P,thermal expansion coefficient α and heat capacity c_V on pressure P and temperature T are obtained.