Abstract: Due to complex working conditions, the inner and outer walls of the oil extraction pipe are prone to damage. At present, the main method of detecting oil extraction pipes is to remove them from the oil well and send them to the back line inspection site for testing, which causes waste of time, manpower, and material resources. The magnetic flux leakage detection method was used tocarry out online detection of oil extraction pipes during the process of lifting or lowering. A tile type magnetization structure was designed and a three-dimensional simulation model was established for magnetic flux leakage detection in oil extraction pipes. In response to the corrosion defects of oil extraction pipes, the size parameters of the defects were changed, and the distribution characteristics of the leakage magnetic field of the defects were studied.　An online magnetic flux leakage detection system was developed for oil well tubing, and online detection tests on oil well tubing were conducted both in laboratories and oilfield operation sites. The test results showed that the system can quickly and efficiently complete online detection of oil well tubing,which provided some references for damage monitoring of oil extraction pipes.