The possible C-Cl bond activation transition states of five proposed mechanisms in CuI/N,N'-bis(2,4,6-trimethoxyphenyl)-oxalamide (BTMPO) catalyzed coupling reaction of chlorobenzene and benzylamine (W. Zhou, M. Fan, J. Yin, Y. Jiang, D. Ma, J. Am. Chem. Soc. 2015, 137, 11942) are compared by DFT calculations, and the favored oxidative addition/reductive elimination mechanism is studied in detail, showing that the rate-determining step is the oxidative addition step in which the auxiliary ligand contains BTMPO only, and then a concerted substitution of the chloride anion on the Cu(III) metal center by deprotonated benzylamine occurs. A general mechanism of Ullmann-type coupling reaction of (hetero)aryl chlorides is proposed according to these calculations.