The invention discloses a method for adjusting the roll axial direction of a multi-diagonal roll straightener, and an upper straightening roll adjusting device of the straightener is set into an axial adjusting mode and a sidewise fixing and vertical adjusting mode. The method comprises the following steps: a, before an axial adjustable bearing seat moves, propping the bearing seat by adjusting a vertical adjustable bolt (7) on a C-shaped bracket; b, loosening the bolt (1) connecting the bearing seat and a turnplate (6); c, realizing axial adjustment of the upper straightening roll device respectively by an axial adjustable bolt A (8) and an axial adjustable bolt B (9) when the adjustable bearing seat moves axially; and d, tightening the bolt connecting the bearing seat and the turnplate (6) firmly when adjustment is in place. The invention has convenient adjustment operation and assembly and disassembly of an upper roll device, can ensure good contact of the bearing seat bottom surface and the turnplate surface so as to avoid straightening precision from being influenced by shock produced in the working process of the straightener, leads the two bearing seats to work synchronously, and has reliable operation and strong market competitiveness and promotion value.