Abstract In the research, vicissitudes of the internal and external geobodies are clarified, and the specific forms of georelations among geobodies and their impacts on the region are also identified. Based on the above analysis, the research divides the development of geopolitical pattern in Southeast Asia before the end of Cold War into five sections, i.e. the earlyancient age, the midancient age, the laterancient age, the modern age and the contemporary age. This paper argues that there are mainly two influencing factors of the evolution of geopolitical pattern in Southeast Asia. One is the particularity of Southeast Asian geography, and the other is the intervention of extraterritorial geobodies: (1) There is a significant geographical distinction between continent and ocean in the Southeast Asia, and this shapes a difference between geopolitical patterns of the two parts. The special geographical conditions have led to fragmentation of political construction in Southeast Asia, and the openness of the ocean makes it easy for nations in Southeast Asia to communicate with the outside world. Therefore, Southeast Asia is vulnerable to intervention of extraterritorial geobodies. (2) The extraterritorial geobodies that influence the evolution of geopolitical pattern in Southeast Asia can be divided into two groups. Some are the neighboring nations, of which the influences on Southeast Asia are stable, and their own vicissitudes shape profoundly the evolution of geopolitical pattern in Southeast Asia. The others are global powers in different historical periods, and these powers exerted great influences on Southeast Asia successively. However, these influences were not continuous, which degraded with the decline of their powers.