Abstract: The technology of magnetostrictive generated guided waves has been applied to nondestructive testing(NDT) widely. It is difficult to detect the small flaw signal because of guided waves dispersion and multimode. According to these characters of the signal, the method based on Duffing chaotic oscillator was presented to detect flaw signal. First, the Duffing chaotic oscillator was set into the periodic state. Then, the signal without pulsed electromagnetic was introduced into Duffing system, and the system was into the same state whether the signal being with or without flaw. When the signal with the pulsed electromagnetic is introduced into system, the system will still in periodic state if it does not include flaw signal. However, if it includes flaw signal, the system will change into chaotic state. Therefore, this method can be employed to identify the small flaw and improves the accuracy of fault detection.