In this paper, the Merten' s equation and dispersion relation of polaritons in the uniaxial crystal had been deduced from the generalized dispersion relation of the phonon-polariton. Raman spectra of every LO, TO mode and oblique phonons in BaTiO3 and Ce: BaTiO3 single crystals have been recorded, the directional dispersion curves are fitted on the basis of Merten's equation. Raman spectra of A1 polaritons with different wave-vector q have been measured and the high and low frequency dielectric constants in both BaTiO3 and Ce:BaTiO3 are calculated. Two broad asymmetry bands in A1(TO) Raman spectra and the mechanics of structure phase transition in BaTiO3 are also discussed. The influence of Ce on the structure of BaTiO3 single crystal are analysed.