Abstract: The technical details of realizing non-destructive testing(NDT) and acoustic emission(AE) monitoring of fatigue damages of aircraft critical structures during full scale fatigue test were introduced.Descriptions were given to the selection of sensor positions based on stress analysis of the structures under supervision,the sensor mounting schemes,sound wave propagation testing,and studies of AE characteristics of the material under investigation,and so on.Discussions were made on the measuring system and on the study of background noise.Special interest was put on the identification of useful AE signals from background noise.Case studies included the monitoring of the central wing and outer panel jointing area,the upper and lower pivots of main landing gears.New approaches to the AE data processing were employed because of the requirement for the real time and in-time monitoring of the structures throughout the fatigue test.By using the combination of trend analysis,time-based,amplitude-based,and spatial filtering techniques,respectively,together with multi-parameter identifications,real time monitoring of these critical structures was realized,proving the effectiveness of current methods.The AE monitoring played an important role for the fulfillment of the full scale fatigue test.