Abstract: Objective: In the construction of an undergroundexcavated metro station with large crosssection, flat roof and straight wall that underpasses the existing metro rectangular interval tunnel, it is necessary to analyze the stress impact of construction process on existing tunnel.Method: Taking the construction of a newlybuilt station similar to the above as research background, the construction of PBA (pilebeamarch) method station project is designed. A finite element analysis software is used to establish a calculation model simulating and analyzing the above construction process of the newlybuilt station. The variation law and locations of maximum principal stress, maximum tensile stress, and maximum shear stress in the existing tunnel during the construction process are investigated. Furthermore, the range of concrete structure plastic failure zone of the interval tunnel is analyzed. The variation trends and locations of the stress monitored and simulated values are compared, and the simulation accuracy and feasibility are confirmed through goodness of fit.Result & Conclusion: With the progress of construction steps, the maximum principal stress, maximum tensile stress, and maximum shear stress in the existing tunnel structure gradually increase. Based on the fieldmonitored results, from step 1 to step 5, the increases in the above three are relatively small. However, from step 5 to step 6, they suddenly increase to 62.15 MPa, 84.62 MPa, and 47.62 MPa, with increase ratios of 315.0%, 351.0%, and 378.1%, respectively. Subsequently, they slowly increase to 68.75 MPa, 89.61 MPa, and 51.03 MPa. Minor cracks and changes are observed on the concrete structural surface of the existing interval structure bottom plate segment b that is near the deformation joint 1. The fieldmonitored data is in good agreement with the simulation calculation results. The monitored results also indicate that adopting appropriate measures to slow down the construction progress and timely implementing supporting measures can effectively prevent the occurrence of cracks on the concrete surface of existing structure, thus protecting the existing tunnel.