The invention discloses a medicine for treating psoriasis and a preparation method for the medicine. The preparation method comprises the following steps of: decocting radix rehmanniae, processed pangolin, rhizoma smilacis glabrae, Angelica sinensis, Salvia miltiorrhiza, radix sophorae flavescentis, subprostrate sophora, pittosporum tobira, golden cypress, cortex mori radices, fructus forsythiae, Caulis Spatholobi, radix scutellariae, pericarpium granati, spina gleditsiae, cortex dictamni, Cyrtomium fortune, cortex moutan, Eclipta alba, Kyllinga brevifolia, tuber fleeceflower stem and liquorice in water to obtain a decoction; concentrating, and then, adding conventional auxiliary materials; adding purified water until the crude drug content is 1g / ml; encapsulating; and sterilizing to prepare an oral liquid preparation. The medicine disclosed by the invention is an effective prescription used for specially treating the psoriasis and can be used for dispelling wind and eliminating dampness, nourishing Yin and dredging collaterals, activating blood and dissolving stasis and improving psoriasis symptoms caused by endocrine disorders and diminished immunologic functions. Through clinical observation, the effective rate of the medicine is 100 percent. The medicine for treating the psoriasis is natural and pure and is safe and nontoxic and does not have dependency.