Abstract: The isolator is an important part of the scramjet engine, which mainly plays the role of isolating the interference between combustion and the intake duct. The complex flow phenomenon in the isolator has always been the focus of research and attention. In this paper, a three-dimensional numerical simulation method is used to study the influence factors of shock train characteristics of the rectangular isolator. The shock train characteristics under the influence of the factors such as different incoming Mach numbers, symmetry or single expansion angle, and wall cavity are analyzed. The results show that under the condition of high Mach number, the length of the shock train in the isolator becomes shorter, the anti-backpressure ability of the isolator is enhanced, and the total pressure loss increases; the shock train structures in the single expansion isolator and the symmetry expansion isolator are different, and the total pressure loss of the flow field after the isolator has nothing to do with the expansion form; after adding a wall cavity to the isolator, two different modes would appear according to the difference in the back pressure, namely the subcritical cavity mode and the supercritical cavity mode, and the shock train structure and flow field parameter characteristics in the isolator are different in the two modes. Under the supercritical cavity mode condition, the anti-backpressure ability of the isolator decreases, and the total pressure loss increases. The research results of this paper can provide reference for the design and test of the isolator and combustion chamber.