Abstract: Taking the geomembrane floating cover of the anaerobic lagoons in the sewage treatment plant as the research object,through the method of experimental investigation,the thermal imaging technology based on solar thermal wave excitation is adopted to detect the crack defects on the high-density polyethylene（HDPE）geomembrane samples. The proposed method utilizes the naturally occurring heat source（solar radiation）as the thermal wave excitation and verifies the feasibility of exploiting short-term fluctuations in solar radiation thermal wave excitation caused by cloud shading for infrared structure health monitoring. In addition,the transient temperature change process is used to compare the infrared thermal image sequence to enhance the temperature contrast of the defect area. The experiment results suggest that the transient temperature response of structures observed using fluctuations in solar radiation can be used to identify crack defects on the geomembrane. This study provides a reliable detection method for improving the reliability of large-area infrared structural health monitoring without the aid of artificial heat sources outdoors.