Abstract: In order to achieve high-precision detection of surface and near surface defects in in-service oil well tubing, a detection system that can detect different types of oil well tubing defects was designed based on magnetic flux leakage detection mechanism and multi-channel data synchronization acquisition technology. The system adopted an array differential sensor layout and corresponding signal conditioning circuit. Firstly, the magnetic flux leakage signal was optimized through variable step size LMS (minimum mean square algorithm) adaptive filtering and dual sensor differential combination algorithm. Then, the adaptive threshold defect recognition and positioning algorithm was used to identify and locate the defects of the oil well rod body. Finally, the upper computer system was designed based on QT and the calculation results were presented in the upper computer. The experimental results showed that the system can effectively detect the location and quantity of oil pipe defects, and the average error of defect detection was within 5%.