Abstract: 300M steel thermal damage specimens were manufactured using laser instantaneous heating. Different levels of thermal damage area could be obtained by adjusting the heating power of the laser. Different thicknesses of chrome were applied to plate on different levels of specimens, and then the specimens were tested by using the method based on Barkhausen effect. The relationship between the thickness of chrome plating layer and the Barkhausen signal was analyzed. From the research, this method could accurately detect the thermal damage under the chrome plating layer. And the sensitivity descends as the thickness increases. The sensitivity would descend seriously when the thickness is more than 150 μm.