Abstract: The pulsed eddy current testing technology is a new branch of the eddy current nondestructive testing and can detect the defect in the metal conductor equipments quickly and easily. Comparing with the conventional single-frequency eddy current technology, the pulsed eddy current contains more flaw feature information in its response signal because of its wider frequency spectrum. Different depths of surface defects were detected and the relationship between the characteristics of the differential signal and the depth of the defects was analyzed, the experiment showed that peak value not only detected the location of the defects, but also indicateed the depths of the defects. Analyzing the characteristics of the first derivative signal, the result illuminated that it was possible to enhance linearity of the pulse eddy current testing system using the peak value of the first derivative signal.