The invention relates to an arc and straight combined horizontal strut for an advertisement display rack, which comprises a substrate and a cover plate capable of bending. Both ends of the substrate and the cover plate are provided with a support piece respectively; and each of the two support pieces comprises a support base, a support cover, a curved pin roll and magnetic steel; the back part ofthe support cover is provided with a chute; the curved pin roll is connected between the middle parts of the support base and the support cover; the magnetic steel is fixed between the support base and the support cover; the support cover is connected to the support base; the side walls close to end heads of the substrate are provided with a pair of pin roll holes respectively; the side walls at both ends of the cover plate are provided with a pair of pin roll holes respectively; the support pieces are inserted into the chute of the support cover and the pair of pin roll holes on the substrate through a straight pin roll so as to be connected with the substrate; and the support pieces are inserted into the pair of pin roll holes on the cover plate through the curved pin roll so as to be connected with the cover plate. The combined horizontal strut supports the both ends of the cover plate through the support pieces to form an arc so as to be used in arc and straight ways. The adjacentcover plates are attracted due to the magnetism on the support pieces, so the combined horizontal strut has simple structure and is convenient to connect.