Abstract: There are complex aerodynamic interference phenomena in parallel stage separation of TSTO (two-stage-to-orbit) vehicles. Understanding the aerodynamic interference characteristics is of great significance for the separation safety design and evaluation of TSTO. In this study, the aerodynamic interference characteristics of the inter-stage flow has been studied in the Φ 0.5 m hypersonic wind tunnel based on the test techniques of pressure sensitive paint (PSP) and temperature sensitive paint (TSP). By solving the difficulty of PSP and TSP measurement under shielding, we obtained a large area of continuous pressure and temperature distribution in high resolution at Mach number 6 for different separation distances. The results show that the head shock wave of the orbit stage directly hits on the surface of the booster stage model, then generates flow separation and multiple reflections between the stages, forming three-dimensional complex shock wave structures. With the increase of the separation distance, the flow field between the two stages presents flow features from small channel flow to large channel flow. The movement of the high pressure and high temperature interference zone between the two stages moves from front to back, with its peak value weakened, which is the main reason for the change of the aerodynamic/torque characteristics of the two stages as well as their pose variation during the separation process.