Abstract: In CPR1000 PWR nuclear power plants, many devices are made of ferromagnetic materials, whose surface defects inspection usually uses the liquid penetration examination. Under the determined environmental conditions and parameters, comparison tests between PT and MT for BOSS welds, 90 ° fillet welds, lap welds, and shaped pieces are carried out respectively, in order to study the feasibility of the replacement of PT with MT. The experimental results show that, for the workpieces made of ferromagnetic materials, MT has a higher detection rate of defects, higher detection sensitivity, and a shorter operating time than PT, and the defective display of MT is more complete and nondiffusible. Therefore, the replacement of PT with MT is feasible and reliable.