The invention discloses a medicine for treating benign prostatic hyperplasia due to damp-retained heat and a preparation method thereof. The medicine is prepared from the following medicinal raw materials: partedleaf violet herb, botrypus virginianus, selfheal, cichory, lygodium japonicum, Indian rorippa herb, spinach beet, fortune loosestrife herb, fringed pink, elaeagnus commutata root, sheathstipe greenbrier tuber and root, earthworm, logwood, Chinese elder, cynomorium songaricum, largeleaf curculigo rhizome, david anemone rhizome, orchidaceae pecteilis, fructus lycii, mimosa pudica, common bombax flower, luisia morsei, hemsleya macrosperma, uncinata spikemoss herb, herba osbeckiae opiparae, slender falsenettle herb, jasminum elongatum, purslane, rattlesnake plantain and ishige okamurae. The medicine has the beneficial effects of mainly clearing heat, removing toxicity and removing dampness with blood promotion and stasis removal, and is mainly used for treating benign prostatic hyperplasia due to damp-retained heat. The medicine is scientifically combined by traditional Chinese medicinal materials with different medicinal properties to achieve ideal treatment effects, is convenient to take and easy to manufacture, has the advantages of simple preparation process, low cost, safety and no toxic or side effect, can be used for directly acting on focuses, is short in healing time, and can prevent relapse after healing.