Abstract: Aiming at the problem that the clamp flexible pipe joint needs to be welded in actual use, a forming process for the end of seamless steel pipe was proposed. The end boss of the clamp flexible pipe joint needs to be welded was directly formed by upsetting the seamless steel pipe. After calculation, it is found that the initial mold cannot be formed by upsetting at one time, so the forming process is simulated by finite element software Deform-3D. It is found that when the end of the seamless steel pipe is deformed at the beginning, the initial die does not play a limiting role, resulting in a depression in the inner wall of the seamless steel pipe end. During the subsequent upsetting process, the metal flows inward to produce a folding gap, which ultimately affects the forming quality. When the punch presses the inner wall of the seamless steel pipe during upsetting, the metal at the transition corner moves forward and eventually forms a bulge, resulting in stress concentration. The maximum stress value is 938.39 MPa. In order to solve the above problems, a bevel was added to the bottom end face of the punch, and the forming process of expanding the hole and then thickening was carried out. At the same time, the core shaft of the punch was changed into a core shaft with taper, and the chamfer was added at the corner of the contact between the die and the seamless steel pipe to facilitate the metal flow forming. The optimized mold successfully changed the flow of metal,solved the problem of folding gap at the end of seamless steel pipe and raised the inner wall of seamless steel pipe while reducing the load of the mold. It is found that the increase of the slope of the punch bottom reduces the overall load during the process of the punch expanding the inner diameter of seamless steel pipe, and increases its final forming load.