Abstract: Characteristics of the shock train motions in a two-dimensional inlet/isolator were investigated in a shock tunnel with a nominal Mach number of 6. The backpressure that supported the shock train was well controlled by using transverse injections into the isolator. High-speed schlieren and wall pressure measurements were carried out. Results show that the reflected shock waves in the inlet/isolator started flow form the background shock waves. As the transverse injections are opened, the downstream flow is accumulated with the increase of the backpressure and the induce of the shock train in the isolator. When the shock train moves upstream under the influence of the high backpressure, the shape and intensity of the leading shock in the shock train are changed by the background shock waves. Because strong adverse pressure gradients already exist near the incident points of the background shock waves, the leading shock of the shock train at the same side would be enhanced for moving upstream quickly. As the shock train is expelled out of the isolator, the leading shock oscillates near the shoulder for a short duration, until the backpressure is increased further to initiate the inlet buzz. When the backpressure is reduced by switching off the transverse injections, the inlet restarts.