为了研究旋转磁场激励下激光焊接裂纹磁光成像在频域内的特征，采用对激光焊接裂纹磁光图像进行2维离散傅里叶变换的方法，进行了理论分析和实验验证，取得了旋转磁场不同励磁强度下激光焊接裂纹的频谱图数据。结合裂纹磁光图的空域特征，对所获裂纹频谱图灰度值为255的点进行统计分析。结果表明，激光焊接裂纹磁光图像的频域特征和空域特征有一定的对应关系;在一个变化周期内（885帧磁光图），对应频谱图上会出现先变小再变大、再变小再变大或相反的变化过程，最终回到初始状态。这一结果验证了旋转磁场下裂纹磁光成像规律的正确性，对激光焊接缺陷的无损检测是有帮助的。

In order to study the characteristics of magneto-optical imaging of laser welding cracks under rotating magnetic field excitation in frequency domain, the method of 2-D discrete Fourier transform for magneto-optical image of laser welding crack was adopted. Theoretical analysis and experimental verification were carried out. Spectrum data of laser welding crack under different excitation intensities of rotating magnetic field were obtained. Combining spatial characteristics of crack magneto-optic maps, statistical analysis was carried out on the points whose gray value of crack spectrum was 255. The results show that, frequency domain characteristics of magneto-optic image of laser welding crack have a certain corresponding relationship with spatial domain characteristics. During a period of change (885 frames of magneto-optic map), the corresponding spectrum map will be a process of first decreasing, then enlarging, then decreasing, then enlarging or the opposite, and finally returning to the initial state. The results verify the correctness of magneto-optical imaging law of cracks under rotating magnetic field. It is helpful for non-destructive detection of laser welding defects.