Taoism stresses the unification of nature and human, and pays much attention to astronomical calendar. Of course the purpose for Taoists to observe astronomical phenomena and prognosticate seasonal changes is to achieve juvenescence and longevity. Nevertheless, it objectively contributed a lot to the development of ancient Chinese astronomical calendar.

In the Sui and Tang dynasties (581-907), many Taoists participated in making astronomical calendar. In the Sui Dynasty (581-618), Taoist Zhang Bin organized the establishment of Kaihuangli (opening the almanac); meanwhile, he wrote a book of 5 volumes concerning the astronomical calendar. In the reign of Tang Emperor Gaozu (the first emperor of Tang Dynasty, reigning in 618-627), Taoist Xue Yi, based on his astrological observations, narked that it was the time for Li Shimin, the king of Qin, to be the emperor. After Li Shimin (the second emperor of the Tang Dynasty, reigning in 627-650) became the emperor, he set up Zifu Temple (purple house), and appointed Xue Yi as the abbot. Meanwhile, a balcony was built in Zifu Temple to observe astronomical phenomena. The forecast made by Xue Yi is quite similar to what is provided by today's national astronomical observatory.

Undoubtedly, the Taoists' astronomical knowledge was just the result of religious activities, and was utilized mostly by emperors and kings to hold religious rites in palaces or to foretell their political prospects. Objectively, it had accelerated the development of ancient Chinese astronomy.

Throughout the whole Tang Dynasty for over 290 years (618-907), the astronomical calendar underwent eight modifications, among which the earliest two were made by Taoists or by people born in Taoist families.