Abstract: It's difficult to detect the hidden internal corrosion of multi-layer structure of aircraft is hidden and difficult to detect in time, which seriously threatens flight safety. Aiming at the difficulty of damage detection in multi-layer structure of aircraft, this paper studies the detection of simulated corrosion defects in multi-layer structure of hard aluminium alloy using far-field eddy current detection technology. The results show that the embedded information of defects can be judged by phase analysis. The number of defect layers is confirmed by the single layer thickness of aircraft skin. Then the corresponding formula is invoked according to the buried depth and layers, so as to obtain the accurate information of defects. That is, the far-field eddy current has high sensitivity. It can realize the localization and quantitative detection of corrosion defects.