The current research of the political geography of the East Jin Dynasty focuses on certain areas of strategic importance such as Yangzhou, Jingzhou, Xuzhou, Guangzhou, etc., while the discussion of the spatial structure of the regime from the perspective of macro political geography is inadequate, among which many issues are covered by the studies of the Six Dynasties or the Southern Dynasties. Considering the particularity of the aristocratic political society of the East Jin Dynasty, it is necessary to examine its political geography, independent from the Six Dynasties or the Southern Dynasties. This paper is a study of the macro political geography of the regime of Emperor Yuan of the Jin, the first emperor of the East Jin Dynasty who started the era of an aristocratic political society south of the Yangtze River. Emperor Yuan’s court, a so-called state co-governed by Wang and Ma, was heavily checked by Wang’s clan, against which Emperor Yuan tried to fight. This paper thereby discusses the distribution and interaction of the military and political geographical units which were a result of the political struggles and military conflicts between the two sides, and then interprets the aristocratic politics of Emperor Yuan’s regime from a perspective of political geography. The regime of Sima Rui, also known as the Jiangdong regime, lasted over sixteen years, including his roles as the head of the East for ten years, King of Jin for one year, and the Emperor of East Jin for five years. During his period as the head the East, the Sima Rui clique conquered the disobedient forces within the territory. Although his group had an ambition of establishing a new regime south of the Yangtze River, his administrative regionalization showed full respect for the falling court of West Jin. After East Jin was founded south of the Yangtze River, the spatial structure of Emperor Yuan’s regime exhibited five political geographical units, including the core zone along the Yangtze River, the protective supporting area, the marginal area, the border area and the occupied area. This spatial structure reflected an aristocratic political form called ″Wang and Ma co-governing the state″. The Wang brothers controlled the core zone along the Yangtze River while Emperor Yuan tried to contend with Wang’s clan by managing the protective supporting areas, neighboring the core zone. The marginal areas, located on the southern and western frontiers, were further marginalized because of the influence of the aristocratic ethos on the one hand, and on the other hand were not efficiently administered due to the sluggish and weak imperial court on the other. The border areas, which were first distributed between the Yellow River and the Huai River then retreated to the south of the Huai River, and the armed forces, predominantly consisting of refugee generals who fought against enemies in these areas, were generally dominated by Emperor Yuan’s court. After the boundary between East Jin and Zhao moved to the south of the Huai River, the newly formed border areas between the Huai River and the Yangtze River were actually connected to the protective supporting areas west of the Yangtze River, and the refugee generals, for their ethnic, national and family interests, usually obeyed the command of Emperor Yuan’s court and became an external military support when Wang Dun occupied the capital. The occupied areas, once the central part of West Jin, were still the nominal territory of East Jin because of the existence of the resistant forces of the Han nationality. With the fall of the resistant forces, the nominal territory eventually faded out of the sight of the Jiangdong regime. As the political manipulator of Jiangdong regime, the aristocratic group did nothing but hypocritically shed a few tears over the areas occupied by ethnic barbarians in North China. These immigrant aristocratic families from the north were resettled in special districts and their homesickness was therefore comforted by these special districts’ same names as their hometowns in North China. After Wang Dun’s rebellion was suppressed, this spatial structure of political geography, which was a result of the political struggles between Emperor Yuan and Wang Dun, was adjusted to be advantageous to the imperial rule in 324 A.D. when Emperor Ming took efforts to strengthen his imperial power.