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The vacuum system for 40 T hybrid magnet superconducting outsert in the Chinese High Magnetic Field Laboratory has been successfully designed, fabricated, installed, and tested. The vacuum system has achieved stable operation after several rounds of optimization. The influence of the pressure and strong magnetic field on the long-term stable operation of the 40T hybrid superconducting outsert was investigated. In the process of structural verification of the vacuum system, the stress distribution of the vacuum system under the influence of assembly, cooling, and quench is analyzed, and the correctness of the analysis results is verified by the theoretical calculation results of circumferential stress. On this basis, the membrane stress, bending stress, and secondary stress were calculated, and the safety of a large vacuum chamber is evaluated by using ASME international vacuum standard code. According to the outgassing test data of the multilayer insulation under real working conditions, the pumping calculation formula was fitted for outgassing rate estimation. The results show that the vacuum system was pumped down from the atmospheric pressure to 5.0 × 10−3 Pa in approximately 72 h and that it worked stably for a fairly long time, affected little by the strong background magnetic field. • The influence of external stray field on the components under high magnetic field is optimized. Some technical difficulties of the large vacuum chamber in the 40 T hybrid magnet system are introduced. • The mechanical analysis is carried out and verified. The reliability and stability are checked by the international standard of ASME Code for evaluation. • The pumping time of the device is divided into four processes for fitting verification. These fitting results can be widely used in the pumping time estimation of the large vacuum system in eastern Asia (23 ± 3 °C, 40%–65% RH). [ABSTRACT FROM AUTHOR]