Abstract: Alternating current filed measurement (ACFM) is an emerging electromagnetic for nondestructive testing technology. Because of skin effect, ACFM is highly sensitive to surface open crack, but critical for non-surface defect. In this paper, the pulse excitation is presented for non-surface crack detection based on alternating current field measurement technique. According to the simulation and experimental results, the wavelet entropy theory is proposed for non-surface defect recognition. Results show that the proposed algorithm can distinguish different buried crack depths effectively.