Abstract: Dandao丹道(Daoist alchemy) is a model for Daoism to combine traditional astronomy with its religious practice. The Sui, Tang and Five Dynasties are the critical periods for Daoism to transform its cultivation mode from outer alchemy to inner alchemy. The relationship between dandao and traditional astronomy in that period can be manifested in two aspects: for ideology, the emerge of dandao was the result of the immortal theory. Its ultimate pursuit is to coordinate with the rhythm of heaven and earth, to achieve the ideal state of unity between heaven and man, and harmony with Dao; as for the practice aspect, both inner and outer alchemy emphasize the realization of the extension and sublimation of human life through the adaptation and reproduction of the operation mode of the celestial universe. Thus, it can be said that the addition of traditional astronomical and calendar knowledge is one of the theoretical guarantees for the long-lasting development of dandao practice.

Key words: Sui, Tang and Five Dynasties, Daoism, Inner-outer alchemy, Astronomy