As power generated using offshore wind turbines continues to increase, maintaining safe operating conditions with respect to the wind turbines becomes increasingly important. The traditional downtime inspection method is costly. This study proposes a novel method for inspecting wind-turbine blades based on thermoelastic stress analysis (TSA) that employs thermal detection of infrared radiation. The necessary condition for TSA is to achieve adiabatic conditions (high-frequency cyclic loadings). However, wind-turbine blades are subjected to cyclic loadings that do not attain high frequencies. To improve the accuracy of the thermal detection of infrared radiation under low-frequency loadings, the classical TSA theory was modified and the correctness of the modified model was verified via fatigue tests. The BLADED wind turbine simulation software was used to analyze the blade thrust, and the thrust force and thrust variation frequency of the blade in the three directions were calculated. The surface temperatures of the wind-turbine blade under low-frequency loadings were analyzed using the modified TSA model. The proposed model can be used to detect stress and damage related to the blade surfaces.