The invention discloses a cancer pain-relieving plaster prepared by a preparation A and a preparation B, wherein the preparation A is prepared by five branches, five skins, one brick, one stone, five cores, and the like; the preparation B is prepared by poria cocos, pinellia ternate, jackinthepulpit tuber rhizome, trichosanthes kirilowii maxim, centipede, zaocys dhumnade, and the like. When the cancer pain-relieving plaster is prepared, the preparation B is added into the preparation A to be decocted for 4.5-5.5 hours, red lead is added to be mixed to pasty fluid, then cold water is added for steeping to releasing fire-toxin, water is changed once one day, and the plaster is obtained after steeping for 7 days. When the plaster is used, the plaster is coated on cotton cloth or plaster paster. The cancer pain-relieving plaster mainly aims at tumour cancers of lung cancer, gastric cancer, liver cancer, pancreatic cancer, colon caner, rectal caner, kidney cancer, bladder caner, breast cancer, cervical cancer, ovarian cancer, esophagus cancer, laryngeal cancer, and the like and is obvious in pain-relieving effect.