This study reviewed the background of Capital Defense Theory emerged in the late of Joseon Dynasty, the construction process of Bukhan Mountain Fortress, arrangement of facilities inside the fortress, and its operating system, focusing on literatures. The 17th and 18th centuries were the innovational period in the late of Joseon Dynasty. The national land was restored from destruction after experiencing two big wars, and there were big changes in agriculture and commercial industry. In the process, the population in the capital city had increased and it was required to fortify the national defense system for the capital city. There were pros and cons conflicts in the government on the issue to build a capital defense system. The Capital Defense Theory discussed in King Sukjong was raised in this situation. It had the purpose not only for defending against invasion of enemies but also for dealing with internal threatening factors. It is assumed that political aspects worked strongly for security of the regime in the background of building the Bukhan Mountain Fortress while the capital fortress was downsized. Capital Fortress Defense Theory that was raised from the early of 17th century changed the national war strategy to make the king escape to Ganghwa Island and the prince move to Namhan Fortress, after the construction of Namhan Fortress was completed in 1626 (4th year of King Injo). The Capital Defense Theory discussed in King Sukjong was accepted when unstable social factors rapidly increased and there were demands for securing safety of citizens and intensifying royal and military power. When the discussion to build Bukhan Mountain Fortress was made in full scale by Shin Wan and Lee Sibaek in 1702 (the 28th year of the King Sukjong), there was confrontation between those who pursued Tangpyong Policy (No-clique policy) and those who were in clique. After then, by a diplomatic letter from Quing Dynasty in 1710 (the 36th year of the King Sukjong ), Joseon had a cause to build the Bukhan Mountain Fortress. The next year, Min Jin-goo was appointed the official in charge of Mt. Bukhan (Gugwan Dangsang) and started to build Bukhan Mountain Fortress. The construction work was led by three military offices. That is, Drill Office (Hoonryon- dogam) built 2,299 feet from Sumun-bukbyon to Yongam Gate; Guemwee-young built 2,821 feet from Youngsam-nambyon to Bohyun Peak; and Yeoyoung- cheong built 2,507 feet from Sumun-bukbyon to Bohyun Peak. Total 7,620 feet was built. Most financial support was provided from governmental offices such as Binyeosa, Hojo, Byungjo, Jinhul-cheong, etc. In addition to that, parts of commodities were supplied from the three military offices for construction. The workforce was recruited from construction workers who were the technicians, citizens, and soldiers who belonged to each military office. The facilities inside the fortress were described in “Bukjanji 北漢誌 (Diary in Bukhan Mountain Fortress)” (1745) written by Seong Neung who was the head of the nation monks (Paldo- docheongseop). The fortress gates consisted of 14 in total – 5 grand gates, 2 small gates, and 7 secret gates (Ahm-moon). The watch platforms (Jang-dae) were established in three places of east, south and north. Among them, East watch platform was located in Sidan Peak and took the role of the supreme command post of the fortress to watch out the detached palace (Haeng-gung) and inside the fortress. Haeng-gung consisted of about 120 buildings including the outer hall, internal hall, and annex buildings. The upper warehouse (Sang-chang) was built at the right of the Haeng-gung and the central warehouse (Jung-chang) was built in front of the Joongheung Temple. The downhill warehouse (Ha-chang) was built inside the west gate. The warehouse for finance (Hojo-chang) was built in front of the Haeng-gung, and the grain warehouse (Pyong-chang) was built at Tangchundae. They had total 140 rooms and could store about 26,000 rice sacks for soldiers. As for watchtowers (Seong-rang), total 143 watchtowers were built – 42 in the district of the Drill Office (Hoonryon-dogam), 60 in the district of Guemwi-young, and 41 in the district of Yeoyoung-cheong.