Provided is a method for producing a high-pressure tank that is capable of suppressing entry of a resin in a stiffener layer into the boundary between a liner body and a mouthpiece, and also offers excellent productivity. The method for producing a high-pressure tank includes disposing a resin sheet on a liner body having a mouthpiece, the resin sheet covering a gap between an outer circumferential portion of the mouthpiece and the liner body, and heating the resin sheet and welding the resin sheet to the mouthpiece and the liner body, to make a liner; and forming a fiber layer around the outer circumference of the liner, the fiber layer being impregnated with a resin, and curing the resin, wherein the softening point of a material constituting the resin sheet is higher than the maximum temperature that is reached by the liner due to heating of the resin.