The invention discloses a preparation method for a medicinal composition for treating skin itch. The preparation method comprises the following steps of: removing Chinese herbal medicines except prepared long-nosed pit viper and pien tze huang powder, performing aqueous extract on the prepared long-nosed pit viper and the pien tze huang powder, and concentrating to obtain a concentrated solution A; performing aqueous extract on the prepared long-nosed pit viper, and concentrating to obtain a concentrated solution B; merging the concentrated solution A and the concentrated solution B, and continuing concentrating to obtain thick paste; and adding the pien tze huang powder and the conventional accessories in the thick paste, mixing and granulating, and drying to obtain all clinically acceptable formulation, such as oral solid preparations comprising tablets, granules, capsules, medicinal tea, powder, pills and the like.