Abstract: By using first-principles plane-wave pseudopotential method of density functional theory,structures and thermodynamic properties of TiO₂ are investigated.Calculated lattice parameters,bulk modulus,and the first order pressure derivative of bulk modulus are consistent with experimental result and theoretical analysis.In a quasi-harmonic Debye model,relative lattice parameters,relative volume,bulk modulus,thermal expansion,and heat capacity under different temperatures and pressures are successfully obtained.