The vibrational modes of BaTiO3 in different crystalline phases have been investigated by means of density functional theory pseudo potential method.The evidence of tetragonal to orthorhombic and orthorhombic to rhombohedral phase transitions present for 8 nm BaTiO3 ceramics further demonstrates that the similar successive transitions in 8 nm BaTiO3 ceramics from rhombohedral to orthorhombic,tetragonal and cubic transitions are as those in coarse BaTiO3 ceramics.