Abstract: With the background of newly-built small clear distance underground excavation interval project in Beijing under-crossing the existing high-speed railway subgrade section, a finite element model is established by using the Madis/GTS finite element software to calculate and analyze the construction process of under-crossing. The characteristics of the horizontal displacement and settlement of the existing high-speed railway subgrade during the construction of the small clear distance underground excavation interval are summarized. The displacement variation pattern is summarized with the actual monitoring data to verify the feasibility of the numerical calculation. Based on the relevant data of similar projects, the subgrade structure and track deformation control indexes of high-speed railway during the construction of under-crossing are put forward.