Investors in international investment arbitration are natural persons and legal persons. The determination of nationalities of the legal persons is mainly based on the criteria of place of incorporation, seat and control. The determination of nationality will affect not only whether the legal persons can obtain the protection of the international investment treaties, but also whether the tribunals have jurisdiction over the cases. The practice of international investment arbitration is usually consistent in the standards of legal persons’ incorporation. However, there are no uniform standards for the determination of seats, which mainly has two kinds of standards: registered office and real or effective seat. In international investment practice, a company that invests as a foreign investor may choose a seat that maximizes its benefits through structural arrangements, which may lead to the abuse of relative treaties and in turn cause the host country to face the risk of being accused, and this increases the difficulty of determining the seats of corporations as well. Therefore, the seats of corporations in international investment arbitration need to be reasonably defined, balancing the interests of investors and host states, so ICSID Convention could protect international investment to a broader extent.