The experimental research on a high-altitude environment experiment of space launch vehicle is important for securing independent technologies with launching space vehicles and completing missions. In the ground test facility, scaled down test models should be used and this is accompanied by various similarities. In addition, free-stream is maintained along the flow direction in a real space launch vehicle having a large length to diameter ratio, but an artificial free-stream recovery is required in the case of the afterbody of the scaled down model in which free-stream is difficult to retain. In this study, high-altitude environment experiment and shock-free technique for free-stream recovery were developed and verified. The effect of the shape of the support for fixing the test model on the flow interference was compared by applying shock-free technique. And, a study was carried out to apply the shock-free technique and the thruster module to confirm the flow interference between the free-stream and exhaust plumes on the base plane, which is the most complicated part of high-altitude environment experiment study. From the results of the flow verification tests, it was confirmed that the flow was replicated with the error of about $\pm 3%$. The error between the slope angle of inclined shockwave of the scaled down transition section model using the shock-free shape and the slope angle of the horizontal plate model, and between the theoretical and the experimental value of the static pressure of the model were confirmed to be 2% and 1%, respectively. As a result, the efficiency of the shockwave cancellation technique has been verified. From the thruster test, not only a shockwave pattern, but a flow-field pattern from the mutual interaction between the exhaust plume and the free-stream undisturbed flow, was experimentally observed.