In engineering practice, structural vibration resistance tests often only record the root mean square (RMS) values of vibration stress, lacking information on the power spectral density function (PSD), resulting in an inaccurate input for response assessment, particularly for predicting vibration fatigue life. This paper proposes a method for generating PSD by combining experimental and finite element analysis, and designs a process applicable to the local improvement and optimization design of structural vibration resistance. Subsequently, a composite component was designed and subjected to vibration resistance tests, modal tests, and simulation analysis, validating the effectiveness of the method from three dimensions: PSD configuration, RMS values, and fatigue life prediction. This method effectively integrates experimental and simulation data, particularly suitable for local improvement and optimization design in the research and development and validation process of product vibration resistance. Finally, taking an airborne drive device as an engineering application case, the PSD generation method and its improved design process were successfully implemented and verified, further demonstrating its practicality and reliability.