Abstract: For seismic analysis of underground structures, different computational models are used in existing studies. The two-dimensional soil model under vertical incident shear wave is performed by comparing different boundary conditions and wave fields selected for the calculation of equivalent input seismic loads. In order to simulate the condition of scattered wave produced by underground structures, the tunnel-soil model is established and its seismic response is calculated by different methods. The comparisons with the analytic solution or the remote boundary solution show that:in the seismic analysis of underground structures, the accuracy of seismic wave input is the highest, and the calculation result is the most reliable only when artificial boundary condition is set on all the cutoff boundaries; and the equivalent input seismic loads are calculated by incident wave field or by free wave field on the boundary with wave incidence, or by free wave field on the boundary without wave incidence.