Abstract: An experimental study on stretch bending of aluminum extrusion was conducted under different pre- and post-stretching elongation. Cross section distortion caused by radial stress during bending process is one of main parameters concerning forming precision. As shown in the test, cross section distorted as the extrusion was bent into contact with the die. Main distortion of cross section is sagging of upper flange. Sagging distribution along the extrusion was given and sagging of middle cross section is not the maximum. It can be seen that the larger is pre- or post-stretching elongation, the larger is cross section distortion. Springback is a common phenomenon during the unloading process, which is influenced by many parameters and difficulty to be eliminated. Pre-and post-stretching elongation can both reduce springback. When pre-stretching elongation exceeds a certain value, its effect on reducing springback is not obvious, which is similar with post-stretching elongation.