The reaction of oxygen atom with chlorofluoromethyl radical has been studied extensively using the G2(MP2) level of theory. The computation reveals an association-elimination mechanism. The addition reaction of O(P-3) with CHClF proceeds to the formation of an energy-rich intermediate CHClFO*. Five product channels of CHClFO* are found: Cl + CHFO, H + CClFO, CClFOH, HF + ClCO, and F + CHClO. The isomer CClFOH can decompose through six product channels: H + CClFO, HCl + FCO, HF + ClCO, Cl + FCOH, F + ClCOH, and OH + CFCl ((1)A'). On the basis of this ab initio potential energy surface, the energy-specific rate constants of the unimolecular decomposition of the activated adduct CHClFO* are used to estimate the branching ratio with RRKM theory. The productions of Cl + CHFO and H + CClFO are shown to be the dominant and competitive reaction channels. The implications of our results are discussed in terms of understanding the atmospheric and combustion chemistry of the CHClF radicals.