A FEM-numerical simulation system is developed to simulate the process of rotary draw bending of tube. The emphasis is to discuss some factors such as tube materials, bending moment of fan-shaped die, pushing force of sliding slot and tube relative bending radius which have an effect on tube bending quality. The quality parameters of ovality, thinning ratio and thickening ratio are the same as the measurement values in the practical production. Some improved methods are put forward to according to the simulation results. The experiment shows that the simulation system can forecast accurately the deformation in the process of tube bending, so the production manufacturing cost decreases greatly.