Type IV damage in power plants is a premature failure that occurs in the softened heat-affected zone (HAZ) of weldment. Eddy-current method is applied to evaluate electromagnetic properties of high-chromium ferritic steels in order to investigate the material changes of HAZ and base metal in Type IV damage evaluation. A pancake-coil impedance model based upon eddy current theory is proposed to evaluate conductivity and permeability. A series of HAZ and base metal specimens of Modified 9Cr-1Mo steel in different heat treatment conditions are experimentally measured and then their conductivity and permeability are estimated. The evaluated results illustrate electromagnetic properties between heat treatment specimens in different test time can be clearly distinguished by presented approach.