International Civil Aviation Organization (ICAO) presented the Ground Based Augmentation System (GBAS) to support differential GPS precision approach and landing and improve the performance of the navigation service at a terminal area. It needs to be validated whether the GBAS meets the requirements of the civil aviation standard. The paper presents a detailed discussion of the processes of the flight validation, including the construction of ground subsystem and airborne subsystem and their methods of flight validation. The result has shown that the testing GBAS is in accordance with the requirements issued by ICAO, and can provide the service of CAT I precision landing.