To investigate the fatigue strength of welded structures under high cyclic loads，a synchronized coupled testing method combining digital image correlation （DIC） and infrared thermography （IR） is employed to simultaneously acquire full-field strain and temperature data on the structural surface，explaining the evolution of structural damage. First，tensile testing is performed on 45# steel specimens，and the patterns of variations in surface temperature and strain during the tensile process are obtained. The temperature characteristics at various stages of the damage process agree well with the material load-time curve，reflecting the different stages of damage in 45# steel. Finally， ultra-low cycle fatigue testing is conducted on GH4061 welded structure used in engines，capturing the entire process of crack initiation，propagation，and fracture under cyclic loading，with synchronized full-field strain and temperature testing and analysis performed. The experimental results demonstrate the feasibility and effectiveness of this method in monitoring fatigue damage in welded structures.