Abstract: The fatigue cracks at weld toes of welded joints mostly take the form of multiple cracks.Carrying out the tensile fatigue tests based on spectrum with variable amplitude loading of cruciform joints. The evolution process of beach marks characterizing the instantaneous front track of cracks is obtained, the existence of multiple cracks is verified. It was found that the multiple cracks at weld toes of welded joints had obvious asynchronous characteristics. By means of finite element simulation technology, several semi-elliptical initial cracks were inserted into the weld toe step by step, and the evolution process of multiple cracks was simulated. The simulation results were consistent with the experimental fracture. The results show that the shape of crack front changes continuously due to crack fusion, but eventually it tends to evolve towards semi-elliptical shape;The life of crack initiation and small crack propagation in welded structures accounts for a large proportion in the whole fatigue process and has an important influence.