Abstract: The vacuum vessel is a critical component to ensure the stable operation of superconducting magnets in cryogenic environments. A relatively high degree of vacuum can remarkably reduce the refrigeration power required for cooling the magnet and mitigate the system heat leakage, thereby maintaining the thermal stability of the magnet under an extremely low-temperature environment. Different from the structural form of conventional vacuum vessels, the vacuum vessel for superconducting magnet applications with magnetic mirror field type is additionally equipped with radial room-temperature ports for plasma observation and valve boxes for cryocooler installation, where the design of wall thickness directly exerts a decisive influence on the operational safety, economic efficiency and overall performance of the vessel. In this study, aiming at the external pressure working condition under the standard atmospheric pressure, an optimal design was carried out for the existing vessel structure. The linearized stress analysis function in the Static Structural module of ANSYS Workbench was adopted, combined with the Box-Behnken experimental design method in Design Expert software. On this basis, the multi-objective optimization research was conducted by using the Response Surface Methodology to obtain the optimal configuration scheme of the vessel wall thickness. The results show that after the structural optimization, the membrane stress level of the vessel is reduced by 40.8%, and the overall mass of the vessel is lightened by 5.05%. This research work provides a reliable theoretical basis and an effective design method for the structural design and optimization of wall thickness for the same type of vacuum vessels, and also offers a feasible technical reference for the structural optimization design of vacuum vessels in the field of superconducting magnet engineering.