Abstract: This paper introduces the principle of magnetic flux leakage in-line inspection and the feature analysis of the magnetic flux leakage signals based on the magnetic flux leakage technology for in-line inspection. This paper uses the method of combining circumferential weld and magnetic circuit method to identify the polarity of characteristic signal, through comparing the consistency of polar curve and the comparison with the size of the characteristic signal and the way of oil-stealing hole, the technology can effectively identify the pipeline oil-stealing hole, the technology can avoid misjudgment and undetected pipeline oil-stealing hole, and provide technical support for pipeline magnetic flux leakage in-line inspection data analysis and signal recognition in the future.