In order to solve the difficult problem of detecting the oxide scales blockage in ferromagnetic boiler tubes，a non-destructive testing method called magnetic disturbance method was proposed．Numerical simulation is used to analyze the magnetic field distribution characteristics of the ferromagnetic boiler tube under the action of two electromagnets placed orthogonally，and experiments have been done to verify the correctness of the simulation results. The acoustic emission technology is applied to collect the sound generated by the hitting of oxide scale towards the tube wall under the magnetic field，thereby establishing the quantitative relationship between the waveform characteristic parameters and the radio of oxide scales blockage area．Test results indicate that the two electromagnets form a unique magnetic field in the pipe that can penetrate the pipe wall and directly attract the oxide scales because of the non-linear characteristics of the magnetic permeability of the ferromagnetic boiler pipe. The attraction limit of this method is as low as 10% oxide scales blockage area. Moreover， the weighted average time of acoustic signals weighted by the absolute value of amplitude can be used to judge whether the ratio of oxide scales blockage area of the inspected pipe exceeds the standard， which indicates the proposed method has engineering application prospects．