Abstract: Based on the variation of sample surface temperature under cyclic load, the deformation and fracture process of welded joints of A514F high strength steel under static load and cyclic load were studied. The fatigue limit of welded joint was evaluated by the temperature inflection point during cyclic elastic/plastic deformation. The results show that the welded joint of A514F steel has a stable ratchet effect under high cyclic stress. According to the inflection point of the temperature stability value under cyclic load, the fatigue limit of the welded joint of A514F high strength steel is determined to be 395 MPa, and the fatigue limit measured by S-N curve is 390 MPa, the difference between the two is 1.28%, and the fatigue limit of the welded joint can be quickly evaluated.