For the Rocket-Based Combined-Cycle (RBCC) engine, the addition of primary rocket jets makes both the flow field and the shock train structure more complicated. In this study, a three-dimensional Detached Eddy Simulation (DES) modeling was employed for the numerical analysis of a full-scale central-strut isolator. The characteristics of shock train for the flight Mach 3 were studied. As a result, under the effect of central high-velocity central jets and different back pressures, the structure of shock train could be changed. At the low back pressure, the expansion wave originated from the trailing edge of the central strut still existed, and one X-type shock wave was formed at downstream. Then the strength of the subsequent shock waves between the parallel jets and the wall in shock train gradually decays. As the back pressure increased, the leading edge of the shock train moved upstream. The shock train was then transformed into two parts: one part was the oblique shock wave generated in the strut section; another was the quasi-normal shock waves formed in the mixing section within the region between the shear layer and the parallel jets. The origination of the first shock wave could cause the generation of the vortexes in the isolator. With the parallel jet addition, as the vortexes were transported downstream, they broke up into small scales and in more random orientation at the back wall of the central-strut. (C) 2017 Elsevier Ltd. All rights reserved.