Abstract: As a critical parameter of sealed enclosures, airtightness directly determines the service performance and reliability of internal precision equipment. It is necessary to further optimize the structure and process of the sealing groove to ensure the O-ring achieves a good sealing effect and operates effectively over an extended period. To reduce testing deviation, error control was implemented during leak detection, and the leak rate calculation method was optimized. Specifically, the proposed calculation method considers both changes during the dwelling period and the impact of leak detection sensitivity on measured values. Furthermore, the total leak rate under different sealing groove parameters was measured through pressure decay leak testing. The influences of sealing groove depth, width, processing method, and surface treatment on air tightness were analyzed, providing engineering guidance for structural design and processing technology of sealing grooves. The results show that groove depth significantly impacts leakage rate, where depth optimization enhances airtightness according to the compression ratio corresponding to the hardness. Besides, groove width has little influence, allowing simplified design approaches such as table lookup or width coefficient calculations. The sealing groove processed by turning achieve lower leakage than that of two-pass milling, with both substantially outperforming that of one-pass milling. Surface analysis indicates polishing remains ineffective below Ra 1.6μm, while blackening treatments elevate the leakage rate. Therefore, it is necessary to protect the bottom surface of the sealing groove during blackening or to perform precision machining on the sealing groove after the blackening.