Abstract: Magnetic flux leakage (MFL) testing method has been successfully applied in the inspection of various ferromagnetic materials. However, the development of modern manufacturing technology and new application areas brought new challenges in the testing speed of MFL testing. The distortion of MFL signals in high speed testing limits the testing speed. Therefore, many researchers studied the mechanism of signal distortion and found that the time-lag in magnetization was the main reason to affect the MFL signal. When the steel pipe passing through the magnetizing coil at a high speed, the eddy current will influence the magnetization of pipe wall and further influence the MFL signal. Based on the mechanism study, methods such as increasing coil length and using multi-stage magnetization have been proposed to reduce the distortion of MFL signals at high speed. Velocity induced eddy current testing method and velocity induced eddy current thermography have also been proposed and achieved good results in high speed testing.