The invention discloses a protective agent of a coal tar hydrogenation catalyst and a preparation method of the protective agent. The protective agent is composed of three parts, namely carriers, active components and assistants, wherein the carriers include aluminium oxide and zirconium oxide in common; the active components include oxides of molybdenum, nickel or tungsten in common and account for 1-10% of total mass of the catalyst; the assistants include potassium and phosphorus in common, and account for 0.5-6% of total mass of the catalyst, and the balance is the carriers. The preparation method comprises preparation of the carrier and preparation of the protective agent. The protective agent has the advantages that the carrier comprises fine holes and thick holes, of which the apertures are relatively concentrated, wherein the thick holes are beneficial to containing metal impurities and carbon residue; a pressure drop of a catalyst bed is reduced, the hydrogenation catalyst is protected, removal of metal impurities such as vanadium is facilitated by the thin holes, the demetallization activity of the protective agent is properly improved, and different pore volumes and hole distribution of carriers can be prepared by adjusting the ratio of two pore forming materials. In addition, the preparation method of the protective agent is simple in technology, and convenient and stable to fabricate.