Abstract: With the increasing speed of the high-speed train (HST), the safety problem associated with the slipstream caused by the unsteady wake of HST is becoming more and more prominent. In order to explore the impact of bogie configurations on the slipstream and unsteady wake of HST, a scaled two-car HST model CRH3 with three different bogie configurations i.e. asymmetric bogies (AB), symmetric bogies (SB) and without bogies but empty cavities (WoB) is numerically simulated using the improved delayed detached eddy simulation (IDDES). Profiles of the time-averaged and root mean square of the slipstream velocity as well as the unsteady wake structures are comparatively analyzed. In addition, the spectral proper orthogonal decomposition (SPOD) method is used for the mode decomposition and the wake flow reconstruction. The results show that a pair of counter-rotating half-loop streamwise vortices shedding alternatively dominates the unsteady wake for all the three bogie configurations. Compared to the SB configuration, disturbances induced by the AB configuration can interact more strongly with the streamwise vortex pair in the wake region, increasing the intensity of alternative vortex shedding and inducing a larger fluctuation of the slipstream velocity. For the WoB configuration, large-scale vortices separated from the bogie cavity and trailing edge result in a wider wake in the spanwise direction and the largest time-averaged slipstream velocity. Furthermore, by enhancing the diagonal similarity of the correlation matrix, SPOD can enhance the pairing of dominant modes, highlight modal peak frequencies and make modal spatial distribution clearer. The above research findings have a certain significance for the optimal design of bogies for HST, and show the advantages of SPOD in analyzing the unsteady wake of HST.