The mechanisms of the Rh(I)-catalyzed alkenylation reaction were investigated by density functional theory (DFT) calculations. Our results show that the CH activation of this reaction occurs through the metal hydride pathway rather than the general concerted metalation deprotonation (CMD) mechanism. The favorable metal–hydride pathway involves CH oxidative addition, alkyne migratory insertion into RhH and CC reductive elimination. Moreover, the consecutive migratory insertion into the RhH and CC reductive elimination is kinetically more favorable than the alkyne migratory insertion into RhC and CH reductive elimination. The CMD pathway is kinetically unfavorable due to the considerably higher barrier of several elementary steps. The improved mechanistic understanding will enable design of novel couplings between hydrocarbons and CH bonds.