Provided is a method for laser additive manufacturing based on keyhole effects. A welding wire and a laser beam are arranged, at certain angles, on two sides of a normal line of a substrate respectively. The laser beam is applied on the welding wire to generate a deep penetration melting keyhole. The welding wire absorbs energy of the laser beam and is heated and melted in a deep penetration melting mode. The welding wire transmits energy to a surface of the substrate to form a cladding layer. The laser beam irradiates the surface of the substrate after passing through the welding wire, and preheats the surface of the substrate in a heat conduction mode.