Guo Moruo viewed the character xi 習 as a combination of yu 羽 and ri 日 and interpreted the meaning by using an image of a bird flapping its wings, practicing flying in the sunny sky. But Tang Lan viewed xi 習 as a combination of hui 彗 and ri 日 based on oracle bone script and said that hui 彗 is a sound sign. Although Guo Moruo’s theory is more widely known, Tang Lan’s theory corresponds to the ancient shape of Chinese characters. In the academic circle of Chinese characters, Tang Lan’s theory is generally accepted. But nothing clear has been discovered about the similarity between xi 習 and hui 彗 in terms of their ancient pronunciation. For this reason, this study attempts to reconstruct the ancient sounds of xi 習 and hui 彗 by using the Zhengzhang-Pan system and the Baxter-Sagart system, both of which are the latest systems to reconstruct ancient sounds. The result of this study is as follows. The ancient sounds of hui 彗 and xi 習 are /*SG^Wibs/ and /*SG^WШb/, respectively.