Butterfly diagram is an essential method for determine the presence of defects in alternating current field measurement. To study the mapping relationship between conventional crack butterfly diagrams and crack profiles, COMSOL Multiphysics was first used to numerically simulate cracks of different sizes, and reconstruction equations for length and depth feature quantities were established. Secondly, through comparative analysis, the corresponding relationship between the characteristic signal and the butterfly diagram was explored, and a mapping equation between the two was further established by combining image processing methods and conventional linear fitting methods. Finally, detection tests were conducted on groove shaped cracks of different sizes of Q235 steel. The experimental results show that the crack profile errors based on length and depth are 5.46% and 6.02%, respectively. The study achieved the reuse of butterfly diagrams, providing important references for defect risk assessment methods.