The rotary-draw bending process of thin-walled rectangular tube is a complex process with the interaction of many factors. The wrinkling may be produced if the process parameters are inappropriate. So, here, based on finite element numerical simulation, and taking the clearances and the frictions between tube and dies as the optimal design variables and the wrinkling height as the optimal objective, the optimization design for rotary-draw bending process of thin-walled rectangular 3A21 aluminum alloy tube has been carried out by using sequential quadratic programming method. Then, the recommended values of the clearances between mandrel, wiper die and bending die and tube, and the friction coefficients between pressure die, mandrel and wiper die and tube are obtained. The achievements of this study are significant to reduce the manufacturing cost and increase efficiency and bending quality.