Effect of the applying twin laser beam on the welding of AZ31 / A5052 dissimilar metals lap joint was studied. The direct welding and the welding with Al12Si filler wire were carried out. Flow behavior of the molten metal was analyzed by FEM simulation. For both welding methods, failure load of the joints increased by applying twin laser beam with reasonable beam distance. Twin laser beam technique could control temperature distribution and flow behavior of the molten metal.