Mercuric chloride supported on activated carbon (HgCl2/AC) is used as an industrial catalyst for the hydrochlorination of acetylene. Loss of HgCl2 by sublimating from the surface of activated carbon causes the irreversible deactivation of mercury catalyst and environmental pollution. In this work, a ligand coordination approach based on the Principle of Hard and Soft Acids and Bases (HSAB) was employed to design more stable low-mercury catalyst. The low-mercury catalysts (4% HgCl2 loading) were prepared by using HgCl2 and potassium halides (KX, X = Cl, I) as precursors. The HgCl2-4KI/AC catalyst showed best catalytic stability than HgCl2/AC and HgCl2-4KCl/AC in the hydrochloriantion of acetylene. HgCl2 could form more stable complex with KI, K2HgI4 as the main active component of the HgCl2-4KI/AC catalyst. The characterizations of XRD and EDX analysis illustrated that the active component of HgCl2-4KI/AC was highly dispersed on the surface of activated carbon. The sublimation rates of HgCl2 from the catalysts verified that the active component with larger stability constant had better thermal stability. Using Hg(II) complexes with high stability constant as the active component may be the research direction of developing highly stable low-mercury catalyst for the hydrochlorination of acetylene. (C) 2017 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.