Abstract: S700MC high-strength steel with 10 mm thickness was welded by single laser+laser arc hybrid welding. The microstructure and mechanical properties of the welded joints with different weld passes were compared and analyzed. The fatigue limit of S700MC base metal was determined to be 350 MPa by the up-and-down method, the fatigue limit of the weld is 172 MPa. The P-S-N curve of the S700MC weld was accurately fitted by the Weibull distribution model and the three-parameter power function S-N model. The results show that the fatigue cracks mainly initiate from the coarse grain zone in the heat affected zone of the weld, which is overheated to form Widmanstatten structure with coarse grains, poor plasticity,low toughness and high hardness. Larger hardness gradient exists in the heat affected zone, which is easy to cause stress concentration and reduce the fatigue performance of the joint.