Abstract: In this paper, a method of dynamic monitoring of the blades in the inner shell of ferromagnetic engine is presented, and the number, rotating speed and damage state of blades in ferromagnetic engine are monitored by eddy current testing method. Two magnetic poles are set on the surface of ferromagnetic casing, and the eddy current testing probe is fixed between the poles. Blades rotate though the eddy current field near the surface, and eddy current signal is induced in the probe and is transferred to the eddy current instrument. The rotor speed can be calculated by the number of eddy current signals per minute. By measuring the amplitude of eddy current detecting signal, the clearance between the blade and the inner surface of the shell can be calculated. The defect of tip surface can be determined by different signal amplitude. Whether the blades bend or break can be determined when the eddy signal is not evenly spaced. The method can solve the problem of blade safety monitoring in the ferromagnetic engine casing.