The invention discloses a medicinal sustained-release preparation for treating osteomyelitis and a preparation method and application thereof. The medicinal sustained-release preparation is prepared by compressing poly DL-lactic acid (PDLLA) and levofloxacin in a ratio. The preparation method comprises the following steps of: A, cutting the PDLLA, placing the PDLLA together with levofloxacin powder with corresponding mass into an organic solvent, and mixing at a constant speed until the PDLLA and the levofloxacin powder are dissolved; B, heating a blend in an oven so as to volatilize the organic solvent, and scraping off the dried blend from the wall of a container; C, cutting the blend into proper blocks, and placing into a metal mould for primary compression, so that the blend blocks are closely combined into a whole; D, heating the mould and the blend in the mould together in the oven, compressing the mould for forming, taking the mould out, putting the mould into a latex glove andputting into tap water for cooling, and demoulding to obtain a blend medicinal tablet of the PDLLA and the levofloxacin; and E, packaging the medicinal tablet by using a plastic bag, and sterilizing by using 60Co25KGy. The method is easy to realize, and the medicinal sustained-release preparation is convenient to take, has an obvious treating effect, high safety and long medicinal effect time, and is suitable to prevent and treat acute and chronic osteomyelitis.