One of the ancient Lingbao scriptures, which are dated to approximately AD 400, the Taiji zuoxiangong qingwen jing claims that the Ritual Master of the Three Heavens and Perfected of Orthodox Unity (i.e. Zhang Daoling), after having studied the venerable and powerful Lingbao fast, deciphered the Zhijiao jing concealed in the celestial scripture known as the Lingbao Five Correspondence Writs. The subject of the Zhijiao jing is a Celestial Master fast called “Fast of the Three Heavens,” referred to as the “Zhijiao fast” in relevant Taoist texts. Most previous scholars thus conjecture that the Zhijiao fast of Celestial Master Taoism appeared prior to the Lingbao fast. This paper has a different view. We believe that the claim that the Zhijiao jing and the fast it prescribes were transmitted by Celestial Master Zhang of the Eastern Han (25-220) is not credible. The Zhijiao fast preserved in the Zhijiao jing was an Orthodox Unity fast invented by Celestial Master Taoists in imitation of the Lingbao fast in the early fifth century. The Taoist fast actually started with the Lingbao fast advocated by the ancient Lingbao scriptures; the other Taoist fasts, including the Zhijiao fast, were basically modeled on the Lingbao fast created from the fifth century on. This paper first presents the primary sources concerned and provides a collection of the fragments of the lost Zhijiao jing, the key textual evidence for our argument. Based on these primary sources, the main body of the paper discusses how and why the Zhijiao fast imitated the Lingbao fast and demonstrates that the Zhijiao fast emerged after the Lingbao fast. The paper aims to reveal through this case study the basic trend in the development of Taoist ritual from the fifth century on: various Taoist scriptural traditions modeled their own rituals on Lingbao liturgy.