The defensive system of the Jilin General’s jurisdiction during the Qing dynasty was the key to maintaining long-term stability in the northeastern frontier. Based on a systematic review of historical sources, this paper analyzes the system from three dimensions: institutions, spatial organization, and dynamic evolution. Rooted in defensive thought and core principles, the system constructed a hierarchical spatial structure centered on the Jilin garrison city, with other garrison cities at various levels forming its supporting framework, and integrated them into an organic whole through an efficient and interconnected courier-road network. Furthermore, the defensive focus of this system was not static; rather, it dynamically adjusted as external threats waxed and waned, moving from Ningguta as the frontier in the early Qing Dynasty, to Jilin as the core in the mid-Qing Dynasty, and then to Hunchun in the late Qing Dynasty, where the focus shifted eastward and then southward. This defensive model combined ideology, structure, and mechanism into a unified whole, while also demonstrating a high degree of adaptability.