This paper examines Koguryo’s ruling methods for the Yanbian (延邊) region of Jilin (吉林) province in China from the fourth century. Yongil, located in northeastern Koguryo (高句麗), was the center of Northern Okgeo (北沃沮) until the third century. Koguryo, advancing into the region, secured a territorial foothold, building a flatland fortress from King Taejo’s (太祖王) rule, and prepared another base, constructing the new fortresses (新城), fortress, during the King Seochon’s (西川王) rule. Total control by Koguryo over the Yanbian region came during the reign of King Kwanggaeto (廣開土王). Sukshin (肅愼) peoples, living in the north, were subjugated, and the northeastern borders were made definite while Eastern Buyeo (東扶餘) was conquered. flatland fortresses and new fortresses were the hubs of Koguryo’s local control of the Yanbian region. The flatland fortresses included Salgiseong (薩其城), a mountain fortress, and Onteukhyeokbuseong (溫特赫部城), a field fortress, both located in present-day Hunchun (琿春) area. new fortresses in a set of Seongsanjasanseong (城山子山城), a mountain fortress, in Yongil (延吉), and Haryonggosung (河龍古城), a field fortress. Koguryo’s control of the region was carried out centering on the transportation roads leading to and from flatland fortresses and new fortresses. The road from Guknaseong (國內城), the capital at that time, going along the eastern coastline, headed towards flatland fortresses, and the inland-bound road from Guknaeseong led to a new fortresses. How Koguryo had ruled the Yanbian region since the fourth century can be seen through the of King Kwanggaeto monument (廣開土王碑) and the dynasty’s control towards the end through gravestone of Goja (高慈墓誌) and the gravestone of Yidain (李他仁墓誌). The existence of a fortress official (柵城都督) shows that a Yoksal (褥薩), a high-ranking local official of Koguryo, was sent for Checksung. A churyogeunji (處閭近支), another local official, was said to have been dispatched to the new fortresses.