Dual-level direct dynamics method is used to study the kinetic properties of the hydrogen abstraction reactions of CH3CHBr + HBr → CH3CH2Br + Br (R1) and CH3CBr2 + HBr → CH3CHBr2 + Br (R2). Optimized geometries and frequencies of all the stationary points and extra points along the minimum-energy path are obtained at the MPW1K/6-311+G(d,p), MPW1K/ma-TZVP, and BMK/6-311+G(d,p) levels. Two complexes with energies less than that of the reactants are located in the entrance of each reaction at the MPW1K/6-311+G(d,p) and MPW1K/ma-TZVP levels, respectively. The energy profiles are further refined with the interpolated single-point energies method at the G2M(RCC5)//MPW1K/6-311+G(d,p) level of theory. By the improved canonical variational transition-state theory with the small-curvature tunneling correction (SCT), the rate constants are evaluated over a wide temperature range of 200–2000 K. Our calculations have shown that the radical reactivity decreases from CH3CHBr to CH3CBr2. Finally, the total rate constants are fitted by two modified Arrhenius expression. © 2012 Wiley Periodicals, Inc.