Abstract:SThis paper introduces a large building construction project with an area of about 30000 m2. When the surrounding buildings have been built, several confined water inrush accidents occurred during the excavation of the last basement foundation pit with an area of nearly 900m2, which seriously affected the project progress. Finally, it is comprehensively compared and selected from the aspects of safety, economy, effectiveness of water stop and impact on existing buildings, Finally, the MJS construction method with small environmental disturbance is adopted for the treatment scheme of flat bottom sealing and water stop at the pit bottom, which effectively solves the problem of confined water inrush. The successful practice of the project can provide reference and useful reference for the solution of confined water problems in similar complex environments.