Abstract: Determine the magnetization operating region is the key problems in the drill pipe detection. This paper analyzed the characteristic of magnetic flux leakage signals and designed the data acquiring system by choosing the Hall Device as the sensor. It summarized the impacts of the flaw type and size to the magnetic flux leakage by analysis of four kinds of magnetic flux leakage. It further obtained the magnetization operating region. Accordingly it could serve as the theoretical guidance for the research and development of drill pipe detection devices.