The butt joints with 6 mm edge and 30°groove were welded by arc and laser hybrid heat source,and the microstructure of the weld zone,coarse crystal zone,recrystallization zone and incomplete recrystallization zone of the laser-arc hybrid welding joint were observed,and the characteristics of each zone were analyzed. According to the characteristics of hybrid heat source,the upper part of the joint is called the arc zone,and the lower part is called the laser zone. The stress levels of 130 MPa、330 MPa、340 MPa、350 MPa、360 MPa and370 MPa were used in the test to form the S-N curve and analyze the crack morphology and the cause of crack source at various stages during the crack propagation process by combining the fatigue test data and the microscopic morphology of the fatigue under the electron microscope.