Abstract: The friction stir butt welding of 1060 aluminum and AZ31B magnesium alloy was carried out.The vertical pressure at different welding speeds was studied by using three-component cutting force test system.The tensile properties of the joints were tested by electronic universal testing machine.The microstructure of the joints and the tensile fracture morphology were observed by using optical microscope and scanning electron microscope respectively.The results show that the change of welding speed causes the vertical pressure change.However, the vertical pressure has an important influence on the weld surface forming, when the welding speed is 110 mm/min, the vertical pressure fluctuation is small, and the weld surface forming is good.The welding speed also has an important influence on the material flow and grain size of the joint, when the welding speed is 110 mm/min, the microstructure of Al/Mg interface in nugget zone has good mechanical interlocking effect, and the grains are fine and uniform.With the increase of welding speed, the tensile strength and elongation of the joint first increase and then decrease.When the welding speed is 110 mm/min, the mechanical properties of the joint are the best, the tensile strength and elongation are 96.5 MPa and 4.2% respectively, and the fracture mode is brittle and ductile mixed fracture.