This thesis presents the numerical simulation results for a submerged floating tunnel (SFT) under hydrodynamic loads and seismic excitation. Time domain simulations are conducted via OrcaFlex and CHARM3D. SFTs with either vertical and inclined mooring lines were evaluated. The SFTs are assumed to have rigid body, and a Morison equation is used to calculate hydrodynamic loads on SFT. Regular and irregular waves are used in the simulations. In particular, the results of the numerical mockup of the regular wave condition is compared with the experimental conditions for validation of the numerical model. Furthermore, regular and real excitation data are applied to the anchor points of the mooring lines to simulate SFTs under seismic loads; also surge, heave, and mooring tensions are all compared. Different trends are obtained between the hydrodynamic and seismic effects. In the hydrodynamic loads, the motion of SFTs with vertical mooring line is more significant than the motion of those with inclined mooring line. Whereas, in seismic displacement conditions, the motion of SFTs with inclined mooring line is more significant than the motion of SFTs with vertical mooring line. Tension in SFT with vertical mooring line is greater than the tension in SFT with inclined mooring line. These results represent the unique behavior of SFTs under seismic excitation when compared with wave conditions, and suggest the SFT concept for seismic situations.