Ultra-thin stainless steel bellows exhibit exceptional elasticity, however, their inherent low thickness-to-diameter ratio and fillet radius lead to a higher susceptibility to defects such as fractures and buckling, thereby impeding their advancement and widespread adoption within the automotive industry. A mechanical model for thin-walled bellows under the combined action of free bulging, internal pressure and axial force was established through theoretical analysis. And the upper and lower limits of intermal pressure, and the relationship between internal pressure and height of bulging wave under different stress and strain states were found. Experimental and numerical simulation were synergistically employed to investigate the influence of initial expansion internal pressure, shaping internal pressure and loading paths on the forming quality of thin-walled bellows. The bellows obtained by the optimal process parameters, with an average outer diameter of Φ70.7 mm, exhibits an error margin below 2%, validating the accuracy of both the theoretical analysis and numerical simulations, this validation serves as a valuable reference for the fabrication of critical automotive components.