Abstract: In production process of the oil and gas or water well,the case-pipes have often been transfigured,dam- aged and corroded due to infection of the ambient condi- tions,thus,influencing the oilfield yields.It is quite nec- essary to find out the reasons of harming case-pipe,pre- vent the area of harmed case pipe from extending,confirm the project for maintaining the case-pipes and prolong the well's life time by improving the scathed case-pipes inspections.The multilayer case-pipes electromagnetic defect detector logging technique uses electromagnetic in- fluence theory to detect the corrosion,transfiguration, fissure and thickness of the case-pipes in the well.In terms of the electromagnetic defect detection log grog ap- paratus from Russia,this paper introduces the multilayer case-pipes electromagnetic defect detecting principle,ap- paratus structure and traits.Logging data from the single case-pipes or multilayer pipes logging revealed this tech- nique's advantages.