Abstract: The space gravitational wave detector contains multiple functional modules inside, such as test masses, electrode cages, and lock-release mechanisms, all of which need to be sealed under ultra-high vacuum conditions. This paper designs a local vacuum sealing technique based on special flange sealing and a uniform force application mechanism. Two types of seal structures are used: knife-edge seals and flat seals. After pumping, hydraulic drive is used to achieve alignment and even pressing of the sealing surfaces, and the vacuum in the sealed chamber is maintained in an atmospheric environment through mechanical fastening. Finite element simulation and experimental indentation comparison show that a 60° knife edge combined with a silver-plated oxygen-free copper seal ring requires about 74% less pressing force than ordinary CF flanges. The three types of seal rings tested have leak rates on the order of 10⁻¹³ Pa·m³/s under hydraulic pressing; after removing the hydraulic pressure, the leak rates of the silver-plated oxygen-free copper ring and C-ring basically remain unchanged, verifying the stability of the force transfer process. Among them, the silver-plated oxygen-free copper ring combines excellent sealing performance, low pressing force requirements, and adaptability to the space environment, making it the best candidate. Compared with traditional vacuum sealing techniques, this method offers advantages such as simpler structural configuration and more convenient bake-out capability, providing a feasible technical approach and experimental reference for future ground-based sealing of gravitational wave vacuum chambers.