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The ?-AlOOH can transport water into the deep mantle along cold subducting slab geotherm. We investigate the hydrogen-bond symmetrization behavior of ?-AlOOH under the relevant pressure-temperature condition of the lower mantle using ab initio molecular dynamics (MD). The static symmetrization pressure of 30.0 GPa can be reduced to 17.0 GPa at 300 K by finite-temperature (T) statistics, closer to the experimental observation of ~10.0 GPa. The symmetrization pressure obtained by MD simulation is related to T by P (GPa) + 13.9 (GPa) = 0.01 (GPa/K) × T (K). We conclude that ?-AlOOH in the lower mantle exists with symmetric hydrogen bond from its birthplace, or someplace slightly deeper, to the core-mantle boundary (CMB) along cold subducting slab geotherm. The bulk modulus decreases with T and increases anomalously upon symmetrization: for ?-AlOOH with asymmetric hydrogen bond, and for ?-AlOOH with symmetric hydrogen bond. Our results provide an important insight into the existent form and properties of ?-AlOOH in the lower mantle.