Abstract: The principle of nationality is shared by ICSID arbitration mechanism and the regime for diplomatic protection; however, there are lots of major conflicts on the contents and requirements between both systems. It seems that article 17 of Draft articles on Diplomatic Protection establishes the priority of ICSID arbitration mechanism over diplomatic protection regime of foreign investors. Article 27(1)of ICSID Convention is constructed on the premise that foreign investors constantly possess single nationality, those investors with multi-nationalities or whose nationality has been changed will face many morasses. Meanwhile, the priority of ICSID arbitration mechanism will seriously undermine the system of diplomatic protection.