Owing to the influence of environmental temperature, pollution, moisture, and other climatic factors, metal components of power transmission and transformation systems are prone to premature failure. Generally, weather-resistant materials are coated on metal components. In view of the shortcomings of the existing methods for measuring the coatings, this study uses lock-in thermographic technology to evaluate the thickness. First, the principle and repeatability of the method were verified using standard coating specimens. The results show that the method is reliable and stable for the evaluation of the coating thickness. Subsequently, a wedged weather-resistant coating sample was tested. The error in the measured thickness was within ±5% of the actual value. Therefore, the phase image can be used to effectively measure and evaluate the thickness and uniformity of weather-resistant coatings.