The invention discloses a roll bending force combination plate shape control method for a six-roll rolling mill, and belongs to the field of mechanical automation control. At present, main wide flat steel six-roll rolling mills are provided with working bending rolls and middle bending rolls. According to the method, a proportional relation between the adjustment quantity of the working bending rolls and the adjustment quantity of the middle bending rolls under different rolling operating conditions is designed, so that a secondary plate shape defect can be controlled when the working bending rolls and the middle bending rolls are adjusted in the same direction, a quartic plate shape defect can be controlled during reverse adjustment, and a high-efficiency and practical roll bending force combination plate shape control method is established for the six-roll rolling mill according to the principle. With the adoption of the control method, rapid and precise control can be performed on the quartic plate shape defect troubling production for a long time by a manual intervention method or an on-line closed-loop system model method.