Based on the Veto Player Theory, the Study discusses the decisions -making Progress of the Taiwans's National Pension Insurance (NPI). We try to answer why the National Health Insurance (NHI) could be introduced in 1994, but the NPI was legislated in 2007 and unlike NHI, the NPI is not a universal insurance, although the debate of NPI in the earlier 1990ties was one of the major driving forces behind the rapid expansion of Taiwanese welfare state. The institutional approach Veto theory, especially the Veto Player Theories which designed by George Tsebelis, was increasingly applied to examines the comparative study of the development of the welfare states. The approach is still seldom applied for Policy studies. The Study is try to fulfilled this vacuum of Taiwanese Social Policy Studies.After examining four periods of decision-making Progress of NPI, we analyze the Power and Preferences of the Veto Players and its structure. In order to apply the Veto Player Theory, we firstly examine the Articles regarding decision-making progress by Constitution and figure out the major players in Taiwan. Secondly, we examine the Strength of the Power and the Preferences of the Players, and discuss the possible roles of the partisan and other type of the veto players. Finally, we apply the absorption rule to combine the veto players and analyze the structure of the veto players. The study confirms the veto player approach can more successfully explain the reasons why NPI forming today's context and why repeatedly delayed the legislating time.