The invention relates to automobile exhaust catalysts, in particular to a preparation method of an automobile exhaust ternary catalyst. The preparation method comprises the following steps: mixing zirconia powder with cerium oxide powder according to a mass ratio, performing ball milling, then adding aluminum oxide powder, ferric oxide powder and manganese oxide powder, and continuing ball milling so as to obtain composite powder; compounding the composite powder and deionized water into slurry, then immersing carriers into the slurry, performing baking and roasting, then immersing the roasted carriers into a palladium chloride ammonia solution, taking out the immersed carriers, and performing drying, roasting and cooling; then immersing the processed carriers into a potassium borohydride solution, and washing the immersed carriers with deionized water; then immersing the washed carriers into a solution prepared from palladium chloride, an ammonia solution, EDTA, hydrazine hydrate and deionized water, performing a reaction, then taking out an reactant, and performing washing and drying. According to the preparation method disclosed by the invention, particles of catalyst powder are refined through the ball milling, and the grain size achieves a nanometer level; besides, ferrum and manganese are added, so that the activity of the catalyst is improved. According to the preparation method disclosed by the invention, palladium plating is also performed on the carriers, so that plating is uniform and compact, and the chemical stability, the hardness and the lubricating property are high.