A method for manufacturing a piston for a vehicle engine, comprising: a piston assembling step of forming a piston assembly by assembling a first piston part, a bonding member and a second piston part, wherein the first piston part has two bonding surfaces (112, 113) separated from each other and extended in a circumferential direction and a first groove formed therebetween, and the second piston part has two bonding surfaces (122, 123) separated from each other and extended in the circumferential direction and a second groove formed therebetween; a piston diffusion brazing step of diffusion brazing the first piston part, the bonding member and the second piston part under an open atmosphere by heating the formed piston assembly; and a piston cooling step of cooling the piston assembly formed by diffusion brazing the first piston part, the bonding member and the second piston part, characterized in that the piston diffusion brazing step is performed in a piston manufacturing device including a partially opened heating zone (Z 1, Z 2) and cooling zone (Z3, Z4), a heater for providing heat into the heating zone, and a moving unit moved in one direction through the heating and cooling zone (Z1-Z4), the piston assembly seated on the moving unit, and wherein in the piston diffusion brazing step, the piston assembly is heated while being moved at a predetermined speed through the heating zone in the one direction by the moving unit; and wherein in the piston assembling step, one surface of the bonding member is in contact with the two bonding surfaces (112, 113) of the first piston part and the other surface of the bonding member is in contact with the two bonding surfaces (122, 123) of the second piston part, a portion of the bonding member being positioned between the first groove and the second groove, such that a diffusion layer is formed on the inner surface of a cooling gallery formed by the first and second grooves (114, 124) in the piston diffusion brazing step. a piston assembling step of forming a piston assembly by assembling a first piston part, a bonding member and a second piston part, wherein the first piston part has two bonding surfaces (112, 113) separated from each other and extended in a circumferential direction and a first groove formed therebetween, and the second piston part has two bonding surfaces (122, 123) separated from each other and extended in the circumferential direction and a second groove formed therebetween; a piston diffusion brazing step of diffusion brazing the first piston part, the bonding member and the second piston part under an open atmosphere by heating the formed piston assembly; and a piston cooling step of cooling the piston assembly formed by diffusion brazing the first piston part, the bonding member and the second piston part, characterized in that the piston diffusion brazing step is performed in a piston manufacturing device including a partially opened heating zone (Z 1, Z 2) and cooling zone (Z3, Z4), a heater for providing heat into the heating zone, and a moving unit moved in one direction through the heating and cooling zone (Z1-Z4), the piston assembly seated on the moving unit, and wherein in the piston diffusion brazing step, the piston assembly is heated while being moved at a predetermined speed through the heating zone in the one direction by the moving unit; and wherein in the piston assembling step, one surface of the bonding member is in contact with the two bonding surfaces (112, 113) of the first piston part and the other surface of the bonding member is in contact with the two bonding surfaces (122, 123) of the second piston part, a portion of the bonding member being positioned between the first groove and the second groove, such that a diffusion layer is formed on the inner surface of a cooling gallery formed by the first and second grooves (114, 124) in the piston diffusion brazing step.