In rotary-draw bending process of thin-walled rectangular tube, cross-sectional distortion is an unwanted byproduct, which is closely related to geometry parameters. To study the effects of geometry parameters on cross-sectional distortion, a 3-D finite-elements model was built under the ABAQUS/Explicit environment, and its reliability was validated by experiments. Then, simulation and analysis of the influence laws of geometrical parameters on cross-sectional deformation degree were carried out. The results show that increases with the increase of b/h and decreases with the increase of R/h when b/h>1. However, R/h has little influence on δh when b/h≤1. And the influence of b on δh is larger than that of h, and the effect of h on δh is larger than that of R.