Hydride ions (H − ) have an appropriate size for fast transport, which makes the conduction of H − attractive. In this work, the H − transport properties of BaH 2 have been investigated under pressure using in situ impedance spectroscopy measurements up to 11.2 GPa and density functional theoretical calculations. The H − transport properties, including ionic migration resistance, relaxation frequency, and relative permittivity, change significantly with pressure around 2.3 GPa, which can be attributed to the structural phase transition of BaH 2 . The ionic migration barrier energy of the P 6 3 / mmc phase decreases with pressure, which is responsible for the increased ionic conductivity. A huge dielectric constant at low frequencies is observed, which is related to the polarization of the H − dipoles. The current study establishes general guidelines for developing high-energy storage and conversion devices based on hydride ion transportation. Compression hinders H − migration in the Pnma phase, but it makes H − migration easier in the P 6 3 / mmc phase of BaH 2 .