From Re eyot and the mainland, Vietnamese residents exploiting the East Sea discovered the Hoang Sa and Truong Sa archipelagos. This is a particularly important basis for the feudal State of Vietnam to establish and exercise national sovereignty over these two archipelagos. Sharing the same administrative territory on the Sa Ky estuary, Re eyot becomes the home space of the Hoang Sa team - the unique force that enforces and protects Vietnam's territorial sovereignty over the two archipelagos of Hoang Sa and Truong Sa, it is a typical locality connecting the mainland and islands. This study clarifies the position and importance of Re eyot on the East Sea international sea route, and its relationship with the mainland; Research on the organization of the management apparatus, economic, socio-cultural life of the Re eyot residents as a special grassroots administrative unit.