The extinction principle of the smoke screen is explained, the infrared extinction coefficient is the basic foundation to assess the infrared extinction performance. The three test methods of the infrared extinction coefficient are introduced: the testing methods of Fourier spectrometer, infrared radiometer and thermal imager, and the testing method of infrared extinction coefficient for thermal imager is discussed further. The thermal imager can assess the extinction performance of the smoke screen materials by testing the extinction coefficient of the materials.