Abstract: The microstructure and mechanical properties of X80 pipeline steel welds by magnetic field-assisted cold metal transfer (CMT) welding were studied. The microstructure and grain orientation were analyzed by optical microscopy(OM)and scanning electron microscopy (SEM).The mechanical properties of the weld were tested by using universal testing machine, Vickers hardness tester and impact testing machine. The results show that after adding magnetic field, the weld microstructure transforms from tempered martensite to acicular ferrite and granular bainite, the weld structure is refined and the tensile strength and impact toughness of the weld are increased. Due to the stirring effect of the magnetic field on the molten pool metal, the coarse columnar crystal structure in the weld is broken, as heterogeneous nucleation point, it promotes the needle ferrite nucleation, and the grains are refined and the mechanical properties of the weld are improved.