Shock tunnels have been used to simulate and study high-speed flow conditions; however, they usually provide a short duration of test time, which is less than milliseconds. In this study, the driver gas tailoring technique was used to extend the shock tunnel test time. The flow and the wave behavior inside the shock tube were summarized. The calculation processes of the tailored driver gas compositions were presented. The filling conditions of the driver tube corresponding to the tailored driver gas compositions were calculated. The test time extension was examined through the measurements of pressure behind the reflected shock wave near the shock tube end wall and pitot pressure at the nozzle exit.