This article is a preliminary study of the silk diagram of the mourning system excavated from Mawangdui tomb three (dated to 168 b.c.e.) in 1973. Although it is the earliest precisely dated document of one of the most enduring social institutions in Chinese history, this mourning diagram has received little scholarly attention. Through analyzing its structure, inscriptions, kinship terms, and cosmological symbolism, and comparing it with relevant Warring States and contemporary Han sources, the author has reconstructed the diagram based strictly on evidence internal to the diagram itself. The author then explains the cosmological and numerological significance of the Mawangdui mourning system, and, through rereading passages in Lun yu 17/21, the “Sannian wen” chapter in the Li ji, the “Li lun” in the Xunzi, and the testamentary decree of Emperor Wen (d. 157 b.c.e.), he discusses the multiple ways of justifying mourning practices during the Warring States and early Han periods and the changing interpretations of the cosmological/numerological basis of the mourning system by later text-based scholars, such as Zheng Xuan and Wang Su. Finally, the author discusses the nature and function of the diagram as the source of ritual diagrams illustrating a text in the Chinese classical exegetical tradition. This Mawangdui diagram is a schematic representation of the mourning system with its basic numerological principles and cosmological significance. As a kinship chart, it illustrates the five degrees of mourning, which characterize the scope of close kinship in early Han China. It depicts a mourning tradition similar to those recorded in the Yi li and the Li ji, but represents differently in degrees of mourning that people, especially married-out daughters and their children, were obligated to observe for the death of a relative. It is thus invaluable for us to understand the historical formation of the Chinese mourning tradition and subsequent ritual manuals and legal codes, and it provides new materials for the sociological study of issues concerning Han family structure, the nature of descent groups, women's position, and patrilinealism.