An experimental study was conducted to develop a system for superorbital high-enthalpy pow simulation with gas injection. The expansion tube X-2 was used as the base facility. The synchronization of the gas injection to the expansion tube operation and the effect of the gas injection on the high-enthalpy flow generation performance are carefully discussed. When hydrogen was injected, the performance of the acceleration tube operation was not degraded, whereas with nitrogen injection the shock speed was significantly decreased. Hypersonic shock layers with gas injection were visualized by the schlieren method. This system is expected to be used as a tool to simulate a hypersonic shock layer with ablation for a reentry capsule.