Abstract: The magnetic leakage detection technology can be applied to the detection of boiler water wall pipe, but the fins of boiler water wall pipe will have an impact on the magnetic leakage detection. Therefore, this paper established a three-dimensional model of water wall pipe with or without fins, and made a comparative analysis. Experimental verification was carried out. The results showed that the leakage magnetic field intensity of the water-cooled wall tube with or without fins increased with the increase of the defect size, and the trend was the same. The existence of the fin will take away part of the magnetic field, so that the strength of the leakage magnetic field at the defect was weakened, and the magnetic leakage signal became smaller. This study can provide theoretical support for the application of magnetic flux leakage detection technology in boiler water wall tube.