The temperature fluctuation of the stainless steel irradiated by a CW CO2 laser is studied. In the experiment, the temperature fluctuation and the temperature rise is measured by the infrared thermal imagers. It is found that the maximum amplitude of the temperature fluctuation is kept constant with the increase of the laser heating time; this is different from aluminum, low carbon steel, epoxylite and polymethylmethacrylate. This characteristic of the stainless steel is determined by the variance of thermal conductivity and thermal diffusivity with the increase of temperature. A thorough study of the effects of the material thermal properties on the temperature fluctuation is needed.