The utility model discloses a large product isostatic pressing auxiliary device which comprises a lower tray, an upper tray, a cylinder sleeve and a plurality of screw and nut groups. The cylinder sleeve is placed between the upper tray and the lower tray and is cylindrical, a plurality of overflow holes are designed in a cylinder wall, both the upper tray and the lower tray are disc-shaped and respectively provided with an annular groove and a radial arc-shaped overflow groove, each annular groove is matched with the cylinder sleeve, and the upper tray, the lower tray and the cylinder sleeve are connected into a whole by the screw and nut groups. When a large product is a ring product, the isostatic pressing auxiliary device further comprises a core rod penetrating the upper tray, the lower tray, the cylinder sleeve and the ring product, one end of the core rod is provided with a boss larger than an annular projection at the center of the lower tray, and the other end of the core rod is provided with a lifting ring capable of lifting. On the premise of ensuring product safety, single productivity is doubled as compared with an original method.