King Seong carried out the large-scale construction transferring the capital from Wungjin (Gongju) to Sabi (Buyeo) in 538. But because most of the Buyeo area was the low swamp in the time, it needed above all to form a site before transferring the capital. Until recently, in addition to the scientific excavation, the relief excavations for the construction of new building or the formation of road were conducted on many sites in the Buyeo area. As a result, many remains which were formed on the low swamp including the temple site of Neungsan-ri, Dongna Castle, the remains of Ssangbuk-ri (280-5 Bukpo, Hyeonnaedeul) and the remains of Gua-ri were identified. Also in these remains, the various engineering construction methods irrespective of the nature of remains were used for the purpose of the soft ground reinforcement as follows: mattress method of construction, pile designation, stone alignment, filing of decomposed granite soil, culverts and storage tanks. Especially, the mattress method of construction and the pile designation are thought to be the traditional engineering construction method at least in that they are appeared since the Three Han Sates era. And these soft ground construction methods had an effect on the construction of reservoir in Japan at the time. In the future, the construction method for soft ground reinforcement shall be concerned and studied further in the architecture and the civil engineering as well as the archeology.