The invention belongs to the technical field of pure traditional Chinese medicines, and provides a plaster for treating osteoarthritis, and a preparation method thereof. The plaster is prepared from the following chinese herbal medicine ingredients in parts by weight: 1000 parts of unprocessed semen strychni, 50 parts of unprocessed squama manis, 50 parts of scolopendra, 50 parts of long-noded pit viper, 50 parts of ground beetle, 50 parts of raw frankincense, 150 parts of raw myrrh, 300 parts of radix angelicae sinensis, 300 parts of caulis sinomenii, 300 parts of raw wild aconite root, 300 parts of radix aconiti lateralis preparata, 50 parts of cornu cervi pantotrichum, 50 parts of ligamentum cervi, 5000 parts of pure sesame oil, and 1300-1400 parts of minium. All the Chinese herbal medicine ingredients are combined for use so as to achieve the effects of dispersing blood stasis and eliminating stagnation, removing evilness, strengthening the body resistance, and strengthening muscles and bones, the applied plaster has the effects of invigorating the blood circulation and diminishing the inflammation, diminishing the swelling, removing dampness and dispelling cold, and relaxing tendons and easing pain, and can fast recover the functions of the affected limb; the plaster points to symptoms of the osteoarthritis, realizes the purpose of treating both principal and secondary aspect of disease and has a considerable effect; especially for the arthralgia aversion to wind and cold, people feel warm and comfortable and spasmodic muscle tendon tissues can be relieved after the plaster is applied for minutes, pain is immediately diminished, and pain basically disappears for no more than ten days, the functions are improved, and the osteoarthritis can be recovered after the plaster is continuously applied.