Abstract: In the magnetic flux leakage and eddy current combined inline inspection technology, the signal of eddy current sensor is not only affected by the type and size of the defect itself, but also affected by the permeability of pipe at the defect. By analyzing the variation range and trend of the relative permeability of the pipe around the typical defects that is located on the inner and outer wall of the pipe with the finite element method, it was found that the relative permeability of pipe in same size inside and outside the defect area and its variation trend are basically the same, and the relative permeability is related to the depth and area of the defect. In addition, the accuracy of the finite element model and the results was verified by measuring the inductance of the measurement coil. Generally, the research results have a guiding significance for distinguishing the defects inside and outside the pipe wall based on the magnetic flux leakage and eddy current combined technology.