Nd∶YAG laser beam butt-welding of invar36 alloy is carried out. The influence of the welding line′s surface, bead penetration and width to the laser parameter is investigated with plate-welding. The composition and hardness of the fusion zone is investigated with the butt-welding of the thickness of 2 mm. The result indicated that: laser power and pulse duration are the main factors which influence the weld bead penetration, weld width and heat affect zone (HAZ). There is a narrow selection range of the welding speed. The defocusing distance mainly affects the weld bead penetration and weld width. The composition of the welding-line has no obviously change, the hardness is appreciably lower than base body. The crystallographic orientation of the welding line had columnar crystals appeared and austenite growth.