The dragon in the Buddhist underground palace is one of the Eight Heavenly Dragon Kings.

Daoist dragon casting, which originated in the Qin and Han dynasties and flourished in the Jin and Tang dynasties, is a sacrificial activity that focuses on "cave heavens and blessed lands" and is performed alongside the worship of mountains and seas. In Daoism, dragons are seen as steeds that help people ascend to immortality and heaven, galloping between the celestial and human realms, and conveying messages from the text to the mysterious and spiritual. Emperor Xuanzong of Tang, a Daoist enthusiast, sent high-ranking Daoists such as Ye Fashan to cast dragons in famous mountains and caves such as Yue Du, Qingcheng Mountain, Dafang Mountain, and Magu Mountain, at least 25 times. Dragon casting moved from the folk to the court and officially became part of the national sacrificial ceremony. In the Dragon Casting Pool under the Water Curtain Cave of Mount Heng, a copper slip from the 26th year of the Kaiyuan era (738) of Emperor Xuanzong of Tang, inscribed with "Zigai Cave Heaven," was discovered, which belongs to Daoist dragon casting. The Dragon King is also one of the Eight Heavenly Dragon Kings in Buddhism. When the Buddha entered Nirvana, the eight kings of the human world, along with the gods and dragon kings, divided the relics. The dragon kings received one-third of the Buddha's relics and placed them in the Dragon Palace, where they built a pagoda for worship. In the Song dynasty, underground palaces for worshipping Buddha's relics or Buddhist scriptures (Dharma relics) were also called "Dragon Palaces" and were adorned with dragon images. In the underground palace of the Jinhua Wanfo Pagoda from the 7th year of the Jiayou era (1062) of the Northern Song dynasty, a stone pillar with the inscription "Eternal Guardian of the Dragon Palace" was unearthed, along with several bronze dragons. In the underground palaces of the Yiwu Jingde Temple from the 7th year of the Yuanfeng era (1084) of the Northern Song dynasty, the Yixing Fazang Temple from the 4th year of the Chongning era (1105), and the Quzhou Kaixian Temple from the 16th year of the Shaoxing era (1146) of the Southern Song dynasty, gold and silver dragons were unearthed.