The rotary-draw bending process of thin-walled rectangular tube is a complex process with large deformation, large displacement and finite strain which makes the defects, such as wrinkling, distortion and crack be easily produced. To study the complex plastic deformation characteristics, a 3D-FE model for the process was built and validated by experiments. Then simulation and analysis of complex plastic deformation characteristics of the process were carried out. The results show that the distributions of stress and strain are symmetric, and its peak values appear in the edges of tube. With the increase of bending angle, the equivalent stress and equivalent strain initially increase and then reach at a stable value, whereas the fluctuant phenomenon of tangent stress is produced. The moving of the neutral plane of stress can be ignored; however, the moving of neutral plane of strain is more obviously.