What is to be done for reunification of the Korean peninsula? Author tried to answer this question through analysis of the North Korean political system in itself. As a result, it is found in this article that North Korean political power seems to rely not on the vast support from the people, but on the tight control mechanism over them. So North Korea, as a state, is very fragile. This article excludes discussion on inter-Korean relations or North Korean policy. The items dealt here are about preparation when reunification is approaching. And while domestic principles on the items may be modified from time to time, they need to be confirmed now. There are vast items to be decided. First of all, constitutional agreement is necessary. It needs to reconfirm that existing constitution replaces the potential reunification constitution by the current National Assembly. Secondly, considering the provincial division of ROK, regional twin-relationships between South Korean and North Korean provinces need to be decided beforehand. Thirdly, based on that,specifics shall be discussed and researched continuously, in order to make more appropriate alternative, gradually. Set up of reunification agenda for the reunified Korean peninsula must repeatedly supplement the third one of the above, while the former two are fixed by the National Assembly.