Abstract: For the problem of wrinkles on the inner arc edge and low forming accuracy for a wide bottom U-shaped frame of a launch rocket after stretch bending, the influence law of stretch amount on the strain on the inner parts under different stretch bending process parameters during the supplementary stretch bending was simulated and analyzed, and the influence law of the process parameters on the surface accuracy of parts after stretch bending was experimentally studied. The simulation results show that when the wrapping angle ranges from 0° to 90°, the strain on the inner parts first decreases slowly, then increases rapidly, and then decreases, and when the wrapping angle is 60°-70°, the strain on the inner parts is the largest. As the stretch amount increases, the strain on the inner parts gradually increases, which helps the parts to stretch deformation and reduces wrinkles. The experiment results show that when the part is not break, the greater the bending force and the stretch amount, the higher the surface accuracy of parts. The wrinkles are effectively eliminated by increasing the stretch amount, and the experiment results are consistent with the simulation results. When the pre-bending force and the supplementary bending force are 80 kN, the pre-wrapping angle is 60°, the supplementary wrapping angle is 90°, and the supplementary stretch amount is 55 mm, the surface accuracy of parts is the highest, and the vertical edge clearance, bottom edge clearance and arc clearance are the smallest, which meets the technical index requirements.