This paper presents the simplified numerical method for predicting the behavior of ground heave and existing tunnel due to open cut. This method uses Steinbrenner's form considering the strain level-dipendency of deformation modulus of ground to calculate the ground deformation and stress, and the beam model supported by ground springs to calculate the deformation and section forces of the tunnel. These calculations are verified by comparing with 3-dimensional finite element analysis and field measurements. Regarding monitoring of existing tunnel during open cut, this paper shows that the numerical method for calculating the real-time section forces of the tunnel is verified by comparing with shell finite element analysis.