Abstract: In order to improve the veracity and reliability of the alternating current field measurement (ACFM), lots of literatures and detection plots were researched in relation to the difficulty of the signal recognition and determination. This paper gained the typical signal influencing factors and corresponding identification plot for ACFM and summarized several practical scanning methods including parallel scanning. The general process of the crack identification was described based on the above research, which helped to improve the accuracy and efficiency of crack identification in engineering project.