Abstract: Magnetic flux leakage testing is an important nondestructive testing method, which is widely used in petroleum, steel, and other industries. In magnetic flux leakage detection, the lift-off value is one of the most important parameters. Generally, from the perspective of protecting the probe or curved surface detection, a certain lift-off value needs to be maintained between the sensor and the workpiece. However, the leakage magnetic field decays rapidly with the increase of lift-off value, which reduces the sensitivity and signal-to-noise ratio of detection. Therefore, how to make the sensor realize high-precision magnetic flux leakage detection under large lift-off has been an important research focus. Firstly, this paper discusses the definition of lift-off value and introduces the influence of lift-off value. Secondly, three elements of large lift-off detection are summarized. They are the source, transmitting medium, and sensors. According to the above influencing factors, many magnetic flux leakage detection methods proposed by domestic and foreign scholars are summarized. In addition, the method based on transformation detection object is also introduced. Finally, the existing problems and the development trend of large lift-off magnetic flux leakage detection methods are discussed.