The combination of the traditional pipebending technology and the CNC technology of machine tool make the pipe bending process automation. However, there is no fixed size and material specifications. Moreover, the nonlinear relationship between the bending moment and the sizes brings troubles in choosing an electric machine of the CNC pipebending device. Therefore, this paper presents a formula to calculate the pipebending moment, for improving the calculating efficiency and reducing the testing cost. The numerical simulation and experimental test were carried out to verify the accuracy of the formula, respectively. The result shows that the presented formula is effective in solving the engineering problems.