In this paper, we examined how large beams were developed in Korea, China, and Japan in the 6th and 8th centuries, and how this pattern affected Korean architecture later. A large inner space was required to symbolize the authority of the emperor and king and to achieve the purpose of enshrinement of a large Buddha statue forming a cluster, and a large beam over 9m was used to implement this. The use of large beams is confirmed from the late 4th century in China and from the late 5th century at the Seoyeongchonsa Temple Site in Nanjing. In Korea, it is identified from the Lecture hall of Neungsan Risa Temple Site in Baekje(567) and from the middle Buddhist shrine Temple in Hwangnyongsa Temple in Silla(584). Goguryeo is presumed to be around the 6th century, a little earlier than that. In Japan, large beams were used for the first time at the the Lecture hall of Bijosa Temple in 588, which was built by a Baekje engineer. From ancient times to the modern era, the inner space length of the Korean, Chinese, and Japanese architecture was exceptional in some cases, but 9-12m was common. This is judged to be the result of the experience of the material limitation of wood and the size of the inner space established in ancient architecture affecting future generations as a precedent.