With low infrared emissivity coating (LIREC) being easy to get bubble, shedding, wear out, scratch, dirt and other problems, the performance state of LIREC should be measured and evaluated in time to ensure the long service life of the LIREC. A portable infrared emissivity measuring instrument and a portable infrared thermal imager used to test the emissivity of shedding, scratching and fouling coating areas at 5 kinds of temperature are adopted. The result shows that the influence of shedding or fouling on the LIREC is comparatively larger, the scratching and the fouling also make the emissivity of LIREC larger. Therefore, the influence degree should be timely and quantitatively measured and evaluated. The measurement results tested by portable infrared emissivity tester are affected by the surface conditions of the measurement area such as surface roughness and so on. The measurement results tested by portable infrared thermal imager are more affected by temperature.