Abstract: The beyond-mean-field model is applied to study the octupole deformation and shape transition in ^114-124Ba. Potential energy surfaces (PES), low-energy excitation spectra, electric transition rates, and probability density distributions in Ba isotopes are systematically analyzed using a quadrupole-octupole collective Hamiltonian (QOCH) model based on covariant density functional theory. The microscopic QOCH model is shown to accurately describe the empirical trend of low-energy positive-and negative-parity states. The theoretical results of PES, low-lying negative-parity bands, rather large B(E3;3₁^- → 0₁⁺), and extended probability density distributions show evidence of strong octupole correlations in ¹¹⁴Ba. ^116,118Ba present as transitional nuclei, while ^120-124Ba are well quadrupole deformed nuclei.