Abstract: Pipelines play an important role in industrial transportation, and conducting pipeline defect detection work can effectively prevent accidents. Research on electromagnetic ultrasonic nondestructive testing technology for pipeline defects was carried out. A guided wave propagation simulation model was established to determine the form, frequency, and number of cycles of the excitation signal. An electromagnetic coupling model was established to analyze the torsional guided waves excited by transducers with different parameters, and the optimal parameters of the transducer were determined. Then, for the characteristic signals of pipeline defect detection, the detection signals were decomposed into direct waves and echo signals based on modal decomposition, and a mathematical model for defect localization was established. Finally, an electromagnetic ultrasonic pipeline detection test platform was built to verify the propagation laws of torsional guided waves, the excitation of guided waves by the transducer, and the defect localization method. The experimental results showed that after modal decomposition of guided wave detection data in pipeline testing, the axial localization error of defects was within 5%.