Abstract: For a further understanding on 3D shock train structure and correlation between 3D and 2D shock trains at Mach 1.5 and 3.0, the SST turbulence model based on Reynolds average algorithm was employed to simulate the 3D and 2D structures of the shock trains in the isolator respectively, of which the mesh sizes were 18 million and 200 thousand, respectively. First, when the full flow state of the nozzle was completely converged, the shock train structure was induced by a linearly increasing back pressure at the outlet. Then, the 3D shock train simulation results in xy-plane and zx-plane perspectives were analyzed. Finally, structures of the 3D shock train in different slices and structures of the 2D shock train were analyzed for comparison. It is found that the shock train at Mach 1.5 is symmetrical in xy-plane and zx-plane perspectives, which is highly similar to the 2D simulation results. However, the shock train at Mach 3.0 is symmetrical in the xy-plane perspective, while it is asymmetrical in the zx-plane perspective. The asymmetrical structure is highly similar to 2D simulation results. Therefore, there is a ″quasi-2D area″ in the 3D shock train. For the shock train at Mach 1.5, the structures in the areas including the central position and a certain range on both sides of the xy-plane and zx-plane perspectives can be approximated as 2D structures (The proportion of ″quasi-2D area″ is about 40%); for the shock train at Mach 3.0, the structures in the areas including the central position and a certain range on both sides of the symmetrical viewing angle can be approximated as 2D structures (The proportion of ″quasi-2D area″ is about 60%).