Abstract: The technology of acoustic emission(AE) real time monitoring the critical structures (including inaccessible components) during aircraft flight loading conditions fatigue test was introduced. In a noise background due to severe shock and vibration, first of all, AE signals were pre-processed based on time filtering, amplitude filtering, and energy filtering as well as based on spatial filtering techniques. After acquiring the pre-processed AE signal, we adopted a new AE signal analysis principle that gave priority to AE diagnostic parameter trend analysis, multi-parameter analysis identifications and further looked for others(including waveform analysis) as assistant method. Real time monitoring of these critical structures was realized, and was successful in predicting a crack initiation in an interlayer of a bolt hole. The mean of AE monitoring played a key role for the fulfillment of the flight loading conditions fatigue test(FLCFT).