Based on concerned historical records, the article conduct research on the names and some issues related to the architectural history of Dien Huu pagoda under the Ly dynasty. The article aims to discuss and bring forward a theory of reproducing the "one pillar" architecture, that is lotus platform, as well as its symbol of the Buddhist worldview. Initially, the author considers that the term "One Pillar Pagoda" (Nhat Tru pagoda) is named for lotus platform by the common people from the seventeenth century on. This is the central part of a makeshift platform (mandala), and that platform is just part of Dien Huu pagoda under the reign of Ly Nhan Tong king. From the centered lotus platform structure, with concentric multi-layer structure of the makeshift platform (two circles of ponds, a circle of corridor, the system of bridges, towers built up in four directions, Four Heavenly Kings system, etc...), and from Buddhist rituals held in this architecture (bathing Buddha, setting free animals...), the author initially considers that makeshift platform is a type of architecture built under mandala scheme, which is a cosmological symbol according to the Buddhist worldview. It can be said that the mandala of Dien Huu pagoda under the Ly Dynasty, in the context of Dai Viet culture as well as the East Asian culture at that time, is a highly symbolic architecture, and also a unique value of the immortal human spirit. So far, many centuries of history have passed, the reproduction of the mandala of Dien Huu pagoda must be interesting and significant to the history and culture of Vietnam.