Abstract: Objective: When a new metro line overcrosses existing lines and encounters shallow and stratigraphically loose and weak layers, it is essential to select appropriate construction methods to effectively control existing line structural deformation caused by the engineering, ensuring existing line operational safety.Method: Based on the project of Beijing Daxing Airport Express Cigezhuang Sta.Caoqiao Sta. rectangular section where the largespan tunnel overcrosses Caoqiao Sta.Jijiamiao Sta. interval on existing Metro Line 10, the control on existing line deformation during construction is studied. Through comparative selection of construction schemes, the FLAC3D software is used to simulate the construction process and predict the structural deformation of existing line tunnel and track bed. The deformation law of existing line structure throughout construction is summarized, and deformation control measures for key construction steps are determined. During actual construction, existing line structural deformation indicators are closely monitored, and a comparative analysis is performed between fieldmonitored and predicted results.Result & Conclusion: Through scheme comparative selection, PBA (pilebeamarch) method is determined for underground excavation overcrossing construction. Deformation control measures are established for key construction steps, including the use of pipe canopies, segmented excavation with balanced unloading, prestressed anchorages, and lowpressure grouting beneath bottom plate. According to the simulation prediction results, the maximum uplift value at existing tunnel structure bottom is 0.41 mm, and the maximum uplift value at the top is 1.72 mm, meeting the control requirement of a cumulative maximum deformation of 2 mm. Based on the fieldmeasured results, existing line tunnel structure uplift is 1.32 mm, horizontal convergence is 1.00 mm, track bed uplift is 1.20 mm, and segment staggered value is -0.04 mm. The absence of existing line structural deformation warnings during construction process indicates that the deformation is within control.