This study evaluated China's model of “One Country, Two Systems” (一國兩制) 20 years into operation and the bilateral relationship between Taiwan and Mainland China ‒ focusing on Hong Kong, Macau, and Taiwan ‒ and examined future prospects. The study is meaningful in that it conducts a more objective evaluation than the previous studies by empirically analyzing data accumulated over the past 20 years of implementation of the One Country Two Systems principle from various perspectives. In addition, it is also a timely study in that it analyzes how the One Country Two Systems arrangement is likely to develop in the future, and what impact this would have, making considerations for changes in China's national strategy during the Xi Jinping period and the competition for hegemony between the U.S. and China. The results of the analysis indicate that over the past 20 years China has been experimenting with the possibility of coexisting different systems in one country, and that the One Country Two Systems arrangement, as a new form of unification which has never been attempted in the history of mankind, has actually shown the possibility of success. However, in recent years, various political contradictions have been exposed in the process of implementing the arrangement, mostly in the Hong Kong society, and the resulting conflict has gradually intensified. While maintaining the current capitalist system for 50 years, Macau is expected to gradually progress in its “Sinicization,” with continuing active economic and social exchanges and cooperation with mainland China. As a result, Macau is expected to be fully incorporated into China's socialist system in 2049, 50 years after the return, but it is likely to remain a city of special character considering Macau's region and its economic structure. On the other hand, the One Country Two Systems arrangement with Hong Kong is expected to undergo a difficult process in the future. In the midst of various conflicts surrounding Hong Kong, the guarantee for Hong Kong’s autonomy is expected to end in 2047 amid efforts on the part of the mainland government to sinicize Hong Kong. And China wants to apply the philosophy of “One Country, Two Systems” to its reunification with Taiwan as well, but in reality this remains very low in possibility.