Abstract:The post-connection underground connecting structure, serving as a critical connecting node between existing underground spaces and new construction projects, poses significant challenges in construction, with water leakage issues in the roof slab being particularly prominent. This paper presents a case study based on the WK14-4 Plot Project (Phase II) at the Jingu Smart Terminal Manufacturing Base. Through on-site investigations, data analysis, and quality management tools such as the Fishbone Diagram, we conducted an in-depth analysis of the causes behind roof slab leakage in post-connected underground structures. Targeted construction countermeasures were subsequently proposed. Following PDCA (Plan-Do-Check-Act) cycle refinements, key outcomes were achieved: Roof slab leakage rate reduced to below 5%. The research findings provide valuable technical references for similar engineering projects, contributing to enhanced quality excellence and effective cost control.