Abstract: By using the circumferential pipe curtain method to expand a subway station within a formed shield tunnel, the construction sequence of the station section and the interval section can be effectively coordinated, thereby alleviating the pressure on the construction schedule. The circumferential steel pipe curtain can form a pre-supporting system, providing safety guarantees for the subsequent excavation and structural construction of the station's main body. This article proposes a new structural system for “shield before expansion” for circumferential pipe curtain subway stations, and uses numerical simulation methods to systematically study the surface settlement laws and the stress conversion characteristics of each structure during the entire station expansion process. The results show that the surface settlement gradually increases during the station construction, reaching a maximum value of 19.59 mm after the construction is completed; the maximum tensile stress of the columns, longitudinal beams, shield lining, and pipe curtain lining ranges from 0.46 to 1.82 MPa; the stress concentration of the steel pipe sheets is at the connection part between the inverted arch and the pipe curtain, with the maximum tensile and compressive stresses being 37.59 MPa and 105.23 MPa respectively, and the stress of each component is lower than the design limit of the corresponding material, ensuring the structural safety and controllability.