Abstract: Electromagnetic testing logging technology can measure the oil tube, casing tubes through oil tube, provided the remaining wall thickness of oil and casing tubes, casing cracks, corrosion, deformation, dislocation and other quantitative and qualitative information to assess the technical status of down hole pipe and guide its operation. Casing damage has a great impact to the bore hole security and oil and gas production, therefore, casing damage detection is very important. This paper describes the principle of electro magnetic testing logging, and explains the applicative effect of electromagnetic with logging interpretation examples.