Abstract: In this paper, a separately magnetizing structure for ground pipeline in petrochemical industry was designed, each unite could be combined and adjusted relative angle to meet the requirement for detection of pipes with different size. 3D numerical model was set up in order to determine the reasonable structure gap of each unit, and the interference of each unite produced was concluded: because of number of units were added, MFL of defect was enhanced for whether mediate unit or sideways unit, and the enhancive rate of mediate unit was greater than sideways and two sideway units have the same enhance. Finally an experiment was established to verify the numerical results and experimental results were coincided to numerical results well.