The present invention belongs to the technical field of constructional engineering safety detection, and provides a method for detecting hollowing of an exterior wall finish layer. The method for detecting a defect of a facade finish layer of a building proposed by the present invention can realize remote detection in the on-site detection operation and avoid high-altitude hazardous operation of personnel, and is simple and convenient in operation. In data analysis and processing, the method not only can overcome the subjectivity and the instability caused by manual color identification of a temperature image, but also can realize batch processing of image analysis through software or conduct real-time detection and analysis.