The invention discloses a medicine for treating psoriasis and a preparation method thereof. The medicine is mainly prepared from the medicines such as dark plum, rhizoma anemarrhenae, minium, madder, curcuma zedoary, pillis ophidiae, rhizoma alismatis and mountain wood at a certain weight ratio. The medicine disclosed by the invention has the functions of nourishing yin to lessen fire, removing stasis and stimulating the menstrual flow, and clearing heat and removing toxicity, and is fast in effect taking, good in curative effect, and free from psoriasis relapse in case of being used for treating psoriasis.