The invention relates to a traditional Chinese medicine for treating diabetes mellitus. The traditional Chinese medicine is prepared from the following raw medicinal materials in parts by weight: 15 parts of rhizoma polygonati, 10 parts of dendrobium officinale kimura ex migo, 10 parts of cortex lycii, 10 parts of semen cuscutae, 10 parts of pyrrosia lingua, 5 parts of rhizoma sparganii, 8 parts of cattail pollen and 5 parts of bamboo shaving. A clinical experiment proves that the traditional Chinese medicine can be used for safely and effectively treating the diabetes mellitus.