The invention relates to a preparation method of a levofloxacin hydrochloride injection. The method comprises the following steps: adding glycerin, lipoic acid and / or sodium calcium edetate, and sodium sulfite into water for injection, adding pre-treated activated carbon used for needles in two batches, and decarbonizing to obtain a solution A; adding levofloxacin hydrochloride into the water forinjection, dissolving, then adding the pre-treated activated carbon used for needles, and decarbonizing to obtain a solution B; adding the solution B into the solution A, supplementing the water for injection to a full dose, adjusting the pH to 4.0-4.6, filtering, carrying out ultrafiltration, sampling and inspecting ultrafiltrate, filling after the product is qualified, filling nitrogen, carryingout fused sealing, sterilizing, carrying out lamp inspection after cooling, packaging, and testing to obtain the finished product. The product prepared by the method is high in content of principal agents and good in stability, no visible foreign matter appears in a storage process, and the color of the product does not change.