The invention relates to a hydrogenation catalyst based on dicyclopentadiene (DCPD) resin undergoing heat polymerization by dicyclopentadiene in ethylene pyrolysis C9 and a preparation method thereof and application. The catalyst takes gamma-aluminium oxide as a carrier, and catalyst active ingredients are palladium, molybdenum and manganese; based on 100% of the total weight of the catalyst, the catalyst comprises 0.5-1.2% of Pd, 10.0-15.0% of Mo2O3, 5.0-10.0% of Mn, and the balance gamma-aluminium oxide. The catalyst is in a strip shape, a clover shape or a sphere shape with a size of phi 3*3-5 mm, and the specific surface area is 100-150 m2/g. The ingredients are loaded on the carrier in a substep mode and are reduced in hydrogen atmosphere, and the activation process is simple and convenient; a fixed bed hydrogenation process is adopted, the resin does not undergo desulfuration pretreatment, and desulfuration and saturation are performed in one step. Hydrogenation reaction is performed in a heat insulation or row tube fixed bed reactor, and DCPD resin solution concentration, feeding temperature, reaction temperature, pressure, volume liquid hourly space velocity and hydrogen/oil ratio conditions are optimized.