Abstract: It is difficult to detect corrosion effectively in the multi-layer structure for traditional eddy current technology because of skin effect. For solving the problem of quantitatively testing of corrosion on subsurface in multi-layer structure, a corrosion NDT system was designed and established after researching and combining the low-frequency and pulsed eddy current technology. Based on transient analysis of detecting signal, peak and zero-crossing times were extracted as the features to measure the volume and depth of corrosion on the subsurface quantitatively. In addition, the length of corrosion was measured quantitatively by analysis of peak curve. It was confirmed that low-frequency and pulsed eddy current technology had extensively applied foreground in NDT of aircraft.