The invention relates to a medicinal composition for treating psoriasis. The medicinal composition comprises the active ingredients of lysozyme and rheum emodin which are in the weight ratio of (1:10)-(10:1). Compared with a common Western medicinal preparation, a lysozyme preparation of the medicinal composition is simple in preparation method and reasonable in compatibility; the two active ingredients give play to respective effects, and meanwhile, can generate a synergetic effect; the psoriasis is treated remarkably; the lysozyme and the rheum emodin are sourced naturally and are safe and non-toxic, and have no side effect; the medicinal composition does not contain a Western medicinal component, so that the medicament has no medicament resistance.