Rehmanniae Radix (Dihuang in Chinese) is a commonly used medicinal herb in a long history, raw Dihuang, dried Dihuang, processed Dihuang and other varieties have been recorded in the classical prescriptions of past dynasties. In order to clarify the origin and variety evolution of different processed products of Dihuang in Chinese classical prescriptions, ancient herbal books were examined in this paper. Both ancient and modern Dihuang is derived from Rehmannia glutinosa Libosch. in Scrophulariaceae, and R. chingii Li has been used as local medication. Dihuang has been cultivated since the Southern and Northern Dynasties, and the cultivation technique was mature in the Tang and Song Dynasties. Huaiqing Prefecture of Henan Province has been regarded as its genuine producing area. "Dried Dihuang" in Shennong Bencao Jing(, Shennong's Classic of Materia Medica) included raw Dihuang and processed Dihuang. Mingyi Bielu(, Alternative Records of Famous Physicians) has described "raw Dihuang" and "Dried Dihuang" separately, in which "raw Dihuang" should be fresh Dihuang in modern times. Bencao Tujing(, Illustration of Materia Medica) in the Song Dynasty has recorded "raw Dihuang" and "processed Dihuang" correspondingly. The "raw Dihuang" was similar to today's raw Dihuang. "Processed Dihuang" has been recorded in the prescriptions of the Qin and Han Dynasties, which was independently described in the Song Dynasty. The processing methods of processed Dihuang were various in the Ming Dynasty. Processed Dihuang mainly refers to the dried products after stewing with wine or steaming until dark, and the processing methods tend to be simplified in modern times. "Raw and dried Dihuang" and "dried and processed Dihuang" have been independently recorded first in ancient herbal books of the Ming Dynasty, which is the raw Dihuang and processed Dihuang, respectively. This paper has sorted out the varieties of Dihuang, providing a basis of herbology for the origin and processing of traditional Chinese medicinal materials of Dihuang.