The utility model relates to an auxiliary pressing device of an angle opening and closing machine for angle iron. The auxiliary pressing device comprises an upper die located in an upper die holder. Auxiliary pressing die plates are arranged on the left side of the upper die and the right side of the upper die and located below the upper die holder. Guiding blocks are arranged on the left side of the upper die holder and the right side of the upper die holder. Guiding rods are sleeved with the guiding blocks. The lower ends of the guiding rods are connected with the auxiliary pressing die plates. Elastic devices are arranged between the auxiliary pressing die plates and the upper die holder. The auxiliary pressing die plates are additionally arranged on the two sides of the upper die, before angle opening and closing is conducted on the upper die, the two ends of the angle iron are pressed first through the auxiliary pressing die plates, and therefore the portion, not opened or closed, of the angle iron can be effectively prevented from warping up and deforming, product quality is ensured, and preparation is well made for the next procedure.