This paper deals with the three- dimensional stretch- bending forming process of rectangular hollow alumi-num profiles,and devises a die design method for the reconfigurable flexible three- dimensional stretch bending.Then,a method of filling blocks of steel into the profiles is proposed to suppress sagging,and a multi- objective optimization model of the forming process is constructed with a springback function and a sagging function as the multi- objective function.Finally,an optimized agent model is constructed by using the Latin hypercube sampling and the response surface method,and the multi- objective optimization of the global solution is carried out by combi-ning the non- dominated sorting genetic algorithm.The results of both the finite element simulation and the experi-ments show that (1) the flexible die can achieve a better three- dimensional stretch bending; (2) the method of filling blocks of steel can effectively suppress sagging; and (3) an optimized combination of pre- stretch and post-stretch can significantly reduce the springback and the sagging,thus,enabling both to reach the allowable range at the same time.