The mechanism of the multichannel reaction CH3NHNH2 (SC1 and SC2) + O → products is investigated theoretically using ab initio and density functional theory, and dynamics properties are explored by a dual-level direct dynamics method. The calculation of the potential energy surface is carried out at the BMC-CCSD//MPW1K/6-311G(d,p) level. Using canonical variational transition state theory with a small-curvature tunneling correction, the rate constants of each channel are evaluated over a wide temperature range of 200–2000 K on the basis of obtained electronic structures and energy information. The total rate constants are calculated from the sum of the individual rate constants taking into account the Boltzmann distribution of two conformers. The reactivity of the H atom located in different groups is compared. © 2013 Wiley Periodicals, Inc.