Abstract: In the process of foundation pit excavation, most cities give a fixed value of deformation monitoring and early warning index according to experience or specifications. A method was proposed to determine the dynamic indicators of deformation monitoring and early warning during the excavation of foundation pits. Taking the foundation pit project of Wuhu Chengnan River Crossing Tunnel as an example, the degradation of groundwater on the soil and the penetration of groundwater were mainly considered. By amplifying the influence of these two factors on the stability of the foundation pit, FLAC^3D software was used to simulate the excavation process of the foundation pit, and the deformation values of the foundation pit in different excavation layers were dynamically analyzed. The maximum horizontal displacement of the supporting structure and the maximum ground settlement were obtained when the foundation pit reached the critical instability state, which were used as the dynamic indexes of the foundation pit deformation early warning. The correctness of the proposed method was verified by comparing the excavation simulation results, monitoring values and specifications of a foundation pit project in Wuhu. The results show that the cumulative horizontal displacement and the maximum cumulative surface settlement increase with the increase of excavation process, and the early warning control value of the surface settlement and the horizontal displacement of the supporting structure should change with the increase of excavation times; The method can effectively determine the dynamic early warning indicators during the excavation process of the foundation pit, which can provide reference for the determination of deformation monitoring and early warning index in the process of excavation of this project and similar foundation pit projects in this area.