With the development of lightweight materials in various fields, there is a need to research and improve the application of aluminum alloys in sheet metal forming, including body covering parts and complex curved aircraft skins. Specifically, the forming quality and formability of complex stepped parts, such as automobile motor shells and oil bottom boxes, should be improved. Therefore, this study is based on the principle of pre-bulging hydromechanical deep-drawing (PHDD), conducting a forming study of 1060-O aluminum plate with stepped parts. First, based on the analysis of stepped parts, a forming device consisting of a hydraulic punch and rigid die is designed, and a PHDD test platform is built to conduct experiments. Second, the effects of pre-bulging parameters on the forming height, wall thickness distribution, and hardness distribution of stepped parts are analyzed. Finally, to obtain parts with good formability under an optimal parameter combination, a four-factor and four-level orthogonal test is designed, and simulation analysis is conducted using DYNAFORM software. The results show that the wall thickness distribution of the stepped parts is more uniform under the PHDD process, and the movable die designed by the forming device can effectively improve the forming height of stepped parts, reaching 28.9 mm. This study has engineering applications for improving the formability and forming quality of stepped parts.