The invention relates to a medicine for treating skin diseases and a preparation method of the medicine. The medicine is prepared from the following raw materials in parts by weight: 20-40 parts of rubia cordifolia, 20-40 parts of peach kernel, 20-40 parts of schizonepetaspike, 20-40 parts of red peony root, 20-40parts of angelica sinensis, 20-40 parts of belvedere fruit, 20-40 parts of fructus xanthii, 20-40 parts of radix rehmanniae, 20-40 parts of fructus forsythia, 20-40 parts of honeysuckle flower, 20-40 parts of bunge corydalis herb, 20-40 parts of rhizoma smilacis glabrae, 20-40 parts of spina gleditsiae, 20-40 parts of platycodon grandiflorum, 20-40 parts of herba leonuri, 20-40 parts of apricot kernel, 20-40 parts of white paeony root, 20-40parts of fructus arctii, 20-40 parts of paeonia suffruticosa, 20-40 parts of cortex dictamni, 20-40 parts of radix rehmanniae praeparata, 20-40 parts of rheum officinale, 20-40 parts of honeysuckle stem, 20-40 parts of bolbostemma paniculatum, 20-40 parts of liquorice, 20-40parts of muskroot-like semiaquilegia root, 20-40parts of caulis spatholobi, 5-25 parts of snake slough, 5-25 parts of cortex phellodendri, 5-25 parts of divaricate saposhnikovia roots, 5-25 parts of cicada slough, 5-25 parts of shikonin, 5-25 parts of ligusticum wallichii, 5-25 parts of radix angelicae, 5-25 parts of bark of Chinese redbud, 5-25 parts of lemna minor, 5-25 parts of flos carthami, 50-70 parts of lalang grass rhizome and 50-70 parts of indian bread pink epidermis. The raw materials are subjected to nano crushing to prepare a capsule or a pill. The medicine has a significant curative effect on skin diseases such as rubella, eczema, skin itching and freckle acnes.