A method of supporting walls of a hanging furnace of a thermal power boiler, in which method, the walls, being formed of vertical water tubes, are supported horizontally at least by means of buckstays, and vertical pillars, located outside the buckstays, are attached to the ground or the foundations of a boiler building. The method includes attaching beams to the outer surface of the water tube walls, parallel with the vertical water tubes of the walls. Buckstays are attached to the outer surface of the beams. The buckstays are positioned substantially perpendicular to the vertical water tubes of the walls. At least two of the walls, located on opposite sides of the furnace, are connected to the vertical pillars by means of the beams and by an attachment connected directly to the beams and to the pillars, in such a way that pressure loads directed perpendicularly to the water tube walls are transferred by means of the vertical pillars to at least one rigid plane surrounding the boiler.