This article studies the role of astronomy in ancient Chinese society and culture from the perspective of the connection between heaven and man. From its very beginning, ancient Chinese astronomy was closely connected with the worship of heaven. Astronomical observation was both activity of heaven worshiping and means of connecting to heaven. In a largely agricultural society, the making of the calendar was the first priority on the ruler＇s political agenda. The astronomical calendar symbolized the “mandate of Heaven” for the ruler. Changing the calendar signified changing of the mandate of Heaven. Thus calendar reform was an important political and religious issue. Based on knowledge of the calendar, the Chinese had developed the cosmological idea that the ruler must follow the ways of heavens in order to maintain an orderly and harmonious society. Dong Zhongshu from the Han dynasty elaborated the theory of the correlation and interaction between Heaven and man. Ancient Chinese astrology was judicial astrology based on this theory ： abnormal astronomical phenomena being considered as omens that were warnings to rulers in their governance of the state. Astrology thus played a very important role in politics and religion in ancient China.