The invention discloses a method for machining a titanium alloy hollow light-weight airfoil and relates to the technical field of welding. The method for machining the titanium alloy hollow light-weight airfoil aims at achieving the effects that the wall thickness of each core lattice of the hollow light-weight airfoil is small, the height of each core lattice of the hollow light-weight airfoil islarge, production efficiency of products can be improved, and manufacturing cost can be lowered. The method for machining the titanium alloy hollow light-weight airfoil comprises the steps of 1, conducting airfoil structure design, wherein the airfoil comprises skin, the internal core lattices and a frame, the internal core lattices comprise rib plates and connecting ribs, the rib plates are in cross connection, and each connecting rib connects the two corresponding crossing rib plates; 2, conducting material preparation, and conducting cutting and cleaning treatment on the skin, the rib plates, the connecting ribs and the frame; 3, conducting laser welding, wherein firstly, laser welding is conducted on the frame and the internal core lattices, so that a framework is formed, and secondly, laser welding is conducted on the skin and the frame; and 4, conducting thermal shaping, wherein after welding is completed, a workpiece is put into a shaping tool.