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This paper represents an attempt to extend the mechanisms of reactions and kinetics of a methane combustion reaction.Three saddle points (SPs) are identified in the reaction CH4 + O(3p) → OH + CH3 using the complete active space self-consistent field and the multireference configuration interaction methods with a proper active space.Our calculations give a fairly accurate description of the regions around the twin first-order SPs (3A’and 3A") along the direction of O(3p) attacking a near-collinear H-CH3.One second-order SP2nd (3E) between the above twin SPs is the result of the C3v symmetry JahnTeller coupling within the branching space.Further kinetic calculations are performed with the canonical unified statistical theory method with the temperature ranging from 298 K to 1000 K.The rate constants are also reported.The present work reveals the reaction mechanism of hydrogen-abstraction by the O(3p) from methane,and develops a better understanding for the role of SPs.In addition,a comparison of the reactions of O(3p) with methane through different channels allows a molecule-level discussion of the reactivity and mechanism of the title reaction.