Abstract: The difficulty for the "tunnel first before shaft" construction method is the construction of the cross pas? sage of the air shaft through the existing shield tunnel segments. It′ s extremely important to choose the appropriate number of excavation benches, bench spacing and breaking method of the segments for the stability of the excavation face, the safety of the adjacent shield tunnel segments and the control of the ground settlement. This paper takes a running tunnel of Xi′an Metro Line 9 as the engineering background, establishes a 3D finite element model for the construction method of "tunnel first before shaft", and carries out tracking simulation of shield tunnelling process and inverse analysis of ground parameters based on the measured ground settlement. The results show that it is quite reasonable to adopt the bench construction method with reserved core soil to excavate the cross passage, in which the number of excavation benches is recommended to be 4 and the bench spacing is recommended to be 3 m. When the cross passage is excavated through the existing shield tunnel segments, the segments on both sides of the junction with the cross passage should be broken first before the segments in the middle, and the joint bolts between the segments in the affected area should be loosened before breaking the segments, so as to reduce the longitudinal and circumferential failures of the segments.