<p>To study the influence of parameters in processes on the hydroforming quality for an automotive rear subframe, experiments were conducted on a CNC pipe bending machine and a 1200-ton hydraulic forming device. These experiments covered pipe bending, pre-forming, and hydro-bulging to assess the forming quality and common defects of the longitudinal arm. Based on the experimental results, numerical simulations of the bending, pre-forming, and hydraulic forming processes were conducted on DYNAFORM platform. The accuracy of the numerical methods was confirmed by comparing the results with the experimental data. The deformation of the pipe in the pre-bending and pre-forming stages was analyzed and summarized to analyze its impact on the final hydroforming quality. The results showed that an appropriate push speed (material feed) helps to reduce wall thinning during the bending process. Additionally, an excessively high bulge near the small bend in the pre-forming mould could cause severe material collapse in the surrounding area, which could not be flattened by internal pressure in later stages, requiring the bulge height to be lowered. Based on the optimized results from the numerical analysis, an optimal longitudinal arm for the frame was successfully trial-produced to provide guidance for the actual production of the longitudinal arm.</p>