Inner wall wrinkle and outer wall thinning are the main defects occurred during thin walled tube rotary bending．The influence of different processing parameters，such as the mandrel extension length e，the clearance between wiper die and tube c，and the mandrel diameter d on the forming quality were analyzed based on numerical simulation method to avoid the defects during tube rotary bending of automotive water cooled tube．The results show that the larger the mandrel extension length e，the greater the thickness thinning r of the outer wall of workpiece，and the wrinkling tendency decreases firstly and then increases．With the increasing of the clearance c，wrinkling tendency increases．The variation of thickness thinning γ is less when the clearance c is small，and when the clearance c increases to a certain value，the thickness thinning γ increases significantly．With the increasing of the mandrel diameter d，the wrinkling tendency decreases，and the thickness thinning γ increases.