A direct dynamics study is carried out for the hydrogen abstraction reaction OH + HBr --> H2O + Br with a small barrier. The geometries and frequencies of all the stationary points are optimized by means of the three different methods, i.e., MP2/6-311G(d), BHLYP/6-311+G(d,p), and MP4SDQ/6-311G(d,p), It is shown that at the reactant side, there is a hydrogen-bonded complex (HBC) with an energy less than that of the reactants, and from the HBC to the products, the reaction system passes through a reactant-like transition state with an energy slightly higher than that of the reactants. To improve the reaction enthalpy-and potential barrier, higher-level energies for the stationary points are made at the PMP4/6-311++G(3df,3pd) and CCSD(T)/6-311+G(2df,2p) levels. The potential energy profile is further refined by performing the CCSD(T) single-point energy calculations along the. minimum-energy path (WP) at the MP4SDQ level. Furthermore, the rate constants and activation energies over a wide range of temperatures 23-2000 K are evaluated by the improved canonical variational transition-state theory with a small-curvature tunneling correction. It is shown that the calculated rate constants are in agreement with the experiments at the temperature regions 249-416, 23-295, 76-242, and 230-360 K and at 1925 K, with a negative temperature dependence below 360 K, and that the variational effect should be considered for the rate constants at high temperatures. Moreover, the tunneling effects are found to contribute significantly to the rate constants at low temperatures.