The invention provides a roll forming design method capable of enabling a roll bite convexity to have linear vibration with a strip width. The method is characterized in that the roll body of a working roll adopts a piecewise curve; the transition parts of the middle part and the edge parts of the roll body adopt second-degree polynomial curves; and the upper and the lower parts of the working roll adopt antisymmetric curves, so as to enable the convexity of a no-load roll bite formed in a transition area to form a strict linear relationship with a corresponding strip width. A mixed variable-convexity roll forming curve adopts a form of a piecewise function containing second-degree polynomials; within the width range required by the design, the roll forming can enable the convexity adjusting ability of the no-load roll bite to form a strict linear relationship with the strip width, and within other width ranges, a quadratic function relationship is formed; and meanwhile, the convexity adjusting ability of the no-load roll bite forms an appropriate linear relationship with the shift amount of the working roll. According to the utility model, the convexity adjusting ability of the roll bite is enabled to form a linear relationship with the strip width within the width range required by the design, so that not only is the convexity adjusting ability of a roll bite of a wide strip not weakened, but also the convexity adjusting ability of the roll bite of a narrow strip is not increased, further, the overall strip forming control ability of a rolling mill is improved.