The mechanisms for the reaction of CF 3 O 2 with atomic hydrogen were studied with ab initio and DFT methods. The results reveal that the reaction could take place on the singlet and triplet potential energy surfaces (PES). For the singlet PES, addition/elimination and substitution mechanisms are determined, and the former one is dominant. The most favorable channel involves the association of CF 3 O 2 with H atom to form CF 3 O 2 H (IM1) via a barrierless process, and then the O–O bond dissociates to give out CF 3 O+OH. The secondary product might be CF 3 OH+O, formed from the O–O bond cleavage in the initial adduct CF 3 O(H)O (IM2). Other products such as CF 3 +O 2 H, HF+CF 2 O 2 and O 2 +CHF 3 are of no importances because of higher barriers. On the triplet PES, only substitution mechanism is located. With higher barriers involving, the channels on the triplet PES could be negligible compared with the channels on the singlet PES.