Abstract Air Defense Identification Zone（ADIZ）, originated in the 1950s, is an area of airspace over water established by the coastal states for the safeguard of national security. Although it is an area established in the air, it starts with the territorial sea baseline. However, as a result of the insufficient economic driving force and the diminished security interests, ADIZ has never established its legal status through treaties or customary international law. This makes the ADIZ, as an expansion of national sovereign rights, can not be guaranteed effectively by the international law and become a “grey area” of national rights. Some words can be used to describe the characteristics of ADIZ, like “residual”, “technical”, “assistant” and “coastal”. According to the principle of reciprocity, any other country that has established ADIZ should not question the regulations of ADIZ in our country. The deep understanding of its nature and the characteristics has important implications for the establishment of ADIZ in our country.
