Abstract: In the internal inspection of pipes, the relative movement between detection device and pipe will cause eddy current. Some factors such as inspection speed, electrical conductivity of pipe, coercivity of magnet and length of magnetizer will influence the intensity of eddy current, and hence affect the MFL testing signal. This paper analyzes the key factors which influence the intensity of eddy current using finite element methods. Afterwards, finite element models with internal and external defects are built up, and the influence of these factors on MFL signal is obtained.