Abstract: In-Flight Security Officer (IFSO) is introduced to combat hijacking and other crimes. The IFSO has been accepted by more and more courtiers and has been playing an important role for the domestic and international aviation security. With the development of international civil aviation, the ICAO started the modernization of Tokyo Convention and promulgated the Protocol to Amend the Convention on Offence and Certain other Acts Committed on Board Aircraft. The IFSO was incorporated into the Protocol. In order to clarify the legal status of the IFSO, the author studied and analyzed history of IFSO's development, legal basis of its establishment and provisions of the protocol to IFSO, then pointed out that IFSO has special legal status because they are representative of the public power of states. It is proposed that the system of IFSO should be established in Chinese domestic law.