Q345 E low alloy steel was welded by copperplated welding wire and non copper-plated welding wire.Microstructure is observed and a pulsating tensile fatigue test is conducted on its welded joints,and the fatigue fracture is scanned and analyzed. The results show that microstructure of the two kinds of welded joints are similar,and there are more carbon-free bainites in the overheated zone of Q345E low alloy steel welded joint welded by non copper-plated welding wire. The fatigue property of Q345E low alloy steel welded joint welded by non copper-plated welding wire is slightly lower,but the difference between the two kinds of welded joints is not significant and the presence of reinforcement significantly reduces the fatigue limit. The microscopic appearance of the fracture shows that the fracture has no obvious defects, the fracture surface is smooth and the source of crack initiation is clear. The crack grows in the propagation zone,and the morphology of the final fracture zone is dimple with different sizes and depths,which is ductile fracture.