This study is to examine the change of the urban area by the geographical category and the castle construction of the Goryeo Dynasty. The understanding on the geographical category of Gaegyeong is connected to the geographical category of ‘Gaeju’, set up when moved the capital to Gaegyeong in 919 (2nd year of King Taejo). At the time, Gaeju was understood in the same concept with Gaegyeong, and the geographical category of Gaegyeong was comprehend by classified the terms such as ‘Donae Sung-Dong Sung-Seo Sung-Nam Sung-Buk Dong-Gyo Seo-Gyo Nam-Gyo Buk-Gyo’. As a result, Gaegyeong [Gaeju] region was divided generally as ‘Donae’ including ‘Gyo’. The geographical demarcation of Gaegyeong was changed newly and made more clear by the constructed the Outer Castle[Naseong] in 1029 (20th years of King Hyunjong). The castle of Gaegyeong was operated under the system of Royal Castle[Gungseong] and Imperial Castle[Hwangseong] after the capital moved, and it would have been built based on the operating system of Later Goguryeo. The category of Royal Castle and Imperial Castle was the area of the palace and administration facilities. The category of Imperial Castle　was divided into the category of Baleochamgseong at the time of King Gungye before Naseong construction, and then it seemed to reduced to the lower half since Naseong was constructed. The construction of Naseong was delayed by the Khitan’s invasions in 1010 (1st year of King Hyunjong) and 1018 (9th year of King Hyunjong) since Naseong construction was discussed at first. It was actively promoted by Kang Gam-chan’s suggestion, and then only completed in 1029 (20th year of King Hyunjong). The completion of Naseong made the regional classification clearly as ‘Donae and Gyo’ from inside and outside of the castle which had been ambiguous all the while. The castle system, eventually, completed over about 100 years since the capital moved to Gaegyeong, was the completion of the National Capital City system that led to ‘Donae-Gyo-Gyeonggi’. It was the foundation on maintaining the status of Gaegyeong even in the ‘Multi-Capitals System’ consisting of Gaegyeong Seogyeong Donggyeong Namgyeong.