The effective differentiation of pipe inner and outer wall defects is the premise of effective quantification of defects. A method of locating and distinguishing pipe inner and outer wall defects in high-speed magnetic flux leakage detection based on dynamic eddy current is proposed. In this method, the defect location is distinguished by the variation characteristics of magnetic field signals in inner and outer walls when the eddy current magnetic field and external magnetic field are coupled. Firstly, the mathematical model of highspeed magnetic flux leakage detection is established, and the eddy current distribution characteristics and the coupling law of eddy current magnetic field and external magnetic field are analyzed. By using the method of finite element analysis, the influence of coupling action law on the magnetization state of the inner and outer wall and the different characteristics of magnetic leakage signal of inner and outer wall defects at different positions are calculated. A high-speed magnetic flux leakage test platform is designed, and the effect of defect discrimination on the inner and outer wall of steel pipe at different running speeds and detection positions is studied experimentally. Results show that when the pipe enters the position of magnetized coil, the direction of the eddy current magnetic field is the same as that of the outer wall of the pipe. But it is opposite to that of the inner wall of the pipe. When the pipe leaves the position of the magnetized coil, the direction of the eddy current magnetic field is the same as that of the inner wall of the pipe, but opposite to that of the outer wall of the pipe. At different detection positions, the variation law of pipe wall magnetic field is obviously opposite, and with the increase of detection speed, the magnetization state is affected more obviously, and the more obvious the difference of magnetic leakage signals between inner and outer walls. High-speed detection can effectively locate and distinguish the defects of the inner andouter wall of the pipe. The experiment results and theoretical analysis have very good consistency