The invention discloses a ladle nozzle casting drainage plug and a using method thereof. The invention belongs to an attachment device of the ladle for starting the casting operation, in particular to a drainage device used for casting molten steel by a brick cup nozzle at the bottom part of the ladle as well as a using method thereof. The drainage device includes a drainage agent and is characterized in that a plug cap and a plug post are connected into a cylinder with variable diameters; a plug cover is arranged on the plug cap; a bottom plate in a mushroom shape is arranged below the plug post; the drainage agent is packaged/or directly connected into the cylinder composed of the plug cap, the plug post, the plug cover and the bottom plate by a soft bag; the plug cap and the plug post are arranged in a guide rod in a sliding way; a haulage rope is hung on the bottom plate. When in use, the plug post is inserted and fixed into the brick cup nozzle; the plug cap is covered above the brick cup. During casting, the drainage agent drains under the effects of the heat and the gravity of the hot molten steel. The invention has the advantages of simple structure and easy manufacturing; being convenient for arranging the drainage plug for a short time; proper dosage of the drainage agent, high intensity, accurate position, large covering area, stable, safe and reliable mounting, avoiding residues from plugging the nozzle, saving the cost for treating the plugging of the nozzle and being beneficial to production.