The invention discloses an open-rack three-roller oblique rolling extender, which solves the problem that axial positions of three rollers are unadjusted and the problem that the offset, generated by assembling and wearing, at the axial position of a roller shoulder is difficult to correct in the prior art. The open-rack three-roller oblique rolling extender comprises an extender base (12), a lower rack (5), left and right lower roller screw-down drive and balance mechanisms and a roller assembly arranged on the lower rack (5), wherein an upper rack (1) is provided with an upper roller screw-down drive and balance mechanism (2), an upper roller box (3) and an upper roller assembly (4); the upper rack (1) is provided with a left upper guide plate mechanism (13) and a right upper guide plate mechanism (14) respectively, and the lower rack (5) is provided with a lower guide plate mechanism (15); and four wedge blocks are arranged on the lateral surface of the upper roller box (3) respectively, and two wedge blocks are arranged between the upper end surface of the upper roller box (3) and the upper rack (1) respectively. The axial positions of the rollers of the invention are adjustable, so that the rolling quality of a pierced billet is improved.