By integrating system theories, geopolitics, strategic studies and historical sociology, this dissertation gets a research approach of dynamics of system changes, to explore the modern East Asian System: patterns, changes and dynamics. As the aspect of system changes, the Opium War (1839) between the British Empire and the Qing Empire led the collapse of the Tributary System, marked the beginning of modern East Asia System. All the Perry¡¦s Black Ship, the Great Game between Britain and Russia, Qing-Japanese War, Russo-Japanese War, the Pacific War, the collapse of Soviet Union and so on affected the changes of modern East Asia System, and gradually shaped into the current East Asian system: the coexistence of trade exchanges and military confrontation. As the aspect of system patterns, after the Opium War, the British became the dominant state of East Asia, and the operating principles of the West European State System replaced the Tributary System. The Great Game brought the first sea-land power game of the East Asia System. Japan Russo-Japanese war let Japan establish a sphere of influence. United States replaced Japan¡¦s sphere after the Pacific War. While the collapse of the Soviet Union, China could rebuild new Tributary System on the base of geopolitics of the Tributary System, and Beijing could become the new vertex in East Asia. Finally, the dissertation argues that the technological innovation, codes of geopolitics and join of numbers which were outside system, are the main dynamics of changes of modern East Asia System. However, with the recovery of the East Asian geo-economy and the rise of China, we should discuss the new dynamics of the future East Asia System.