Abstract: In this paper, an defect detection method in steel plates was proposed based on abnormal geomagnetic imaging. First of all, the spatial geomagnetic information of the defect specimen area made on the steel plate was collected, the component information of the three directions of the geomagnetic field is obtained, and the abnormal geomagnetic image was finally formed. Through the analysis and processing of the images of different directions of geomagnetism, the defect dectection in steel plate was achieved and the effectiveness and reliability of the abnormal geomagnetic imaging method for the defect detection of steel plate defects were verified.