Active carbon (AC)-supported AuCl₃ catalysts are considered the most promising materials for acetylene hydrochlorination. However, there is no consensus on the reaction mechanism. In this paper, the mechanism and reaction steps of Au(I)-catalyzed acetylene hydrochlorination have been investigated by theoretical calculations. The results show that C₂H₂ assists in the electrophilic addition of HCl, facilitating a change between the Au(I) and Au(III) redox couple. The linear structure of AuCl is proposed to form a tetracoordinated five-membered ring transition state, which is accompanied by the oxidation of Au from Au(I) to Au(III). Besides, we explored and compared the reactivity and energy difference between Au(III)- and Au(I)-catalyzed acetylene hydrochlorination. The DFT calculations indicate that a strong combination between the Au center and ligands and the favorable hydrogen-transfer angle (close to 180°) significantly enhance the activity of the AuCl₃/AC catalyst. We also investigated the change from AuCl₃ to AuCl, which suggests that the process of decomposition of AuCl₃ to AuCl is highly possible. These understandings and explanations also open up an intriguing route to design a novel ligand, which is promising to maximize catalytic performance in acetylene hydrochlorination by increasing the stability of Au(III) in the catalytic cycle.