In this paper,the flexible 3D stretch- bending (FSB) process is investigated,and the mathematicalexpressions of the formed parts are put forward.Then,a method to adjust the flexible fundamental units (FFU)and a calculation algorithm of clamp stretch- bending trajectories are proposed by analyzing the deformation processin the horizontal and vertical directions.By considering the multipoint control of the FFU envelop shape,theadjustment parameters of multi- points dies (MPD) are defined,and the geometric relationship between the FFUand the workpiece is established.Moreover,an interpolation method based on cubic B- spline is presented todescribe the envelop shape of MPD.Based on the above- mentioned geometric relationship and MPD adjustmentparameters,the arc stretch- bending trajectories of the clamp are calculated.Finally,3D stretch- bending experi-ments of the L- section aluminum profile are conducted.The results show that the formed part is of a measured con-tour error of less than 0.7%,which indicates that the proposed methods are practical.