The invention provides a mould for manufacturing a U-shaped rubber ring, belongs to the technical field of moulds, and solves the problem so as to prolong the service life of a middle mould. The mouldcomprises an upper mould, the middle mould and a lower mould, wherein the middle mould is in a disc shape; an annular slice part protruding along the radial direction is arranged on the peripheral surface of the middle mould; a cavity is formed among the slice part, the upper mould and the lower mould; a blank placement table is arranged on the lower mould; a pressing table located correspondingto the blank placement table is arranged on the upper mould; the table surface of the pressing table and the table surface of the blank placement table are planes and are in parallel; a blocking surface upwards extending from the table surface of the blank placement table is arranged on the outer side of the blank placement table; and the slice part and the cavity are located on the inner side ofthe blank placement table. The mould still adopts a mould pressing process; and without increasing the cost, through changing the pressed position of a blank during the mould pressing process, the pressed time and the pressed force of a slice of the middle mould are greatly reduced, so that the slice part of the middle mould is not easy to deform and damage.