This paper investigates the synthetic mechanism of trifluoroiodomethane (CF 3 I) in the reaction of trifluoromethane and iodine via vapor-phase catalytic reaction. It is suggested that CF 2 carbene is the key intermediate and is formed in the pyrolysis process of CHF 3 at high temperature. However, in pyrolysis of CHF 3 under activated charcoal (AC) existing conditions, no C 2 F 4 was detected. H 2 and 2-methyl-2-butene could not trap the CF 2 carbene. When treating the remained compounds on the used AC with H 2 , CH 4 is formed on the process. It is proposed that CF 2 carbene combines with AC strongly and transfers into CF 3 radical on heat. In addition, it is found that the AC is not only the catalyst supporter to form CF 3 I, but also a co-catalyst to promote the formation of CF 2 carbene and CF 3 radical.