The invention discloses a high-stability composite mercury catalyst for hydrochlorination of acetylene. The catalyst comprises the following components: 100 parts of active carbon serving as a carrier, 1-15 parts of mercuric chloride serving as a main catalytic component and 0.1-6 parts of auxiliary component, wherein the auxiliary component is one of chlorides of potassium, barium and lithium or a mixture of multiple of the chlorides, or one of chlorides of strontium, chromium and praseodymium or a mixture of multiple of the chlorides. According to the invention, the problems of the current mercuric chloride catalyst that the thermal stability is low, mercury in the catalyst is easy to volatilize and lose, the service life is short and the environmental pollution is serious are solved. The catalyst disclosed by the invention has the advantages of good dispersibility and high thermal stability, wherein the stability is improved by 0.1-0.5 times compared with that of the pure mercuric chloride catalyst; and moreover, the service life of the catalyst is prolonged, the production cost is lowered, and the pollution is reduced.