The invention discloses a traditional Chinese medicinal composition for treating diabetes mellitus and a preparation method of the traditional Chinese medicinal composition, and belongs to the technical field of traditional Chinese medicines. The invention aims at providing the traditional Chinese medicinal composition for treating the diabetes mellitus, which is rapid to take effects, short in treatment course, good in therapeutic effect, low in toxic and side effects and not easy for recurrence, as well as the preparation method of the traditional Chinese medicinal composition. The traditional Chinese medicinal composition consists of 29 traditional Chinese medicines, namely radix et rhizoma rhei, radix glycyrrhizae preparata, radix scutellariae, radix rehmanniae preparata, rhizoma dioscoreae, radix adenophorae, rhizoma coptidis, rhizoma anemarrhenae, radix ophiopogonis, rhizoma polygonati, fruits of Chinese wolfberry, radix polygonati officinalis, rhizoma atractylodis, cortex phellodendri, fruits of Chinese magnoliavine, radix codonopsis, radix puerariae, radix trichosanthis, raw radix astragali, herba potentillae discoloris, herba paederiae, semen sojae praeparatum, hirudo, radix notoginseng, seeds of acanthopanax senticosus, stem of dendrobium officinale, winged euonymus twig, herb of Apocynum venetum L. and folium ginkgo. The traditional Chinese medicinal composition has the advantages of being short in treatment course, free from toxic and side effects and not easy for recurrence; the traditional Chinese medicinal composition has a good therapeutic effect on primary diabetes mellitus, secondary diabetes mellitus and diabetes mellitus complications; and the effective rate of the traditional Chinese medicinal composition reaches 90% or above.