In order to measure the coating thicknesses on various substrate materials at a high speed and a large area,an active infrared thermographic technique was presented.A light pulse was used to heat to the surface of the coating and an infrared camera was utilized to capture the surface temperature change on real time.For a translucent coating,visible light could not be absorbed well on the surface,so a water-soluble black paint was painted on the surface of the coating.Compared with the differential lnT -lnt curves without painting the coating,the thickness of the painted coating can be measured according to the peak time of second differential ln T - ln t curves.Experiment results indicate that the translucent coating after painting satisfies infrared testing requirements,and the measurement precision is 0.09 mm for the thickness ranges of 0.8-1.7 mm.These data show that the infrared testing can be used in measurement of the coating thickness at high speeds,large areas,noncontact and quantification.