Abstract: Since the 1990s, Japans two major political system reforms, which have continued intermittently and are still on its extended line, have promoted the transformation of Japans political system and changes in the political environment, and also promoted the centralization of the Liberal Democratic Party. In the Liberal Democratic Party, the function of the informal organizations represented by factionalism has weakened, the importance of the executive department centered on the president has increased, and the power has concentrated on the executive department centered on the president. In the actual political operation, the two major institutional effects of the political system reforms, namely the expansion of the power of the Prime Minister and the concentration of the Liberal Democratic Party presidents power, interacted and influenced each other, leading to the phenomenon of “prime ministerial dominance”. The emergence of “Abe Strong One” is a symbol of the maturity of the Liberal Democratic Partys centralization. The power of the powerful prime minister (president) still has no effective control over the Senate. Different institutional arrangements, such as the election system of the House of Representatives, the term of office of parliamentarians, and the legal authority conferred on it by the Constitution, make the Senate highly independent. At the same time, the Liberal Democratic Party is indispensable for the joint control of the Komeito Party in the Senate as long as it does not control the majority of seats in the Senate alone. The prime minister is required to cooperate with the Liberal Democratic Party, which must joint to pass bill with the Komeito party in the Senate. The Senate has become the “Achilles’ heel” of the Liberal Democratic Party.

Key words: Japanese politics, political system reform, Liberal Democratic Party, centralization