Abstract: With the continuous increase of the flight altitude of advanced aircraft in the future, the requirements for wind tunnel test simulation ability are constantly increasing, such as the lower vacuum running ability. The conventional multistage ejection system can no longer fully meet the operation requirements. In order to improve the height simulation range of the wind tunnel test, CAAA designed a vacuum exhaust branch based on the original equipment of its newly built Ф1.2 m hypersonic wind tunnel to realize the pressure vacuum mode operation of the wind tunnel. The wind tunnel system debugging and testing results show that after the wind tunnel capacity is improved, each subsystem works normally and the system performance reaches the design target, and the hypersonic flow field condition at the altitude above 40 km with Mach number 5–8 is realized. The flow field index in the uniform area of the test section meets the relevant requirements of the aerodynamic test of the National military standard GJB 4399-2002. It provides a test platform for the study of aerodynamic characteristics of aircraft and complex hypersonic flow at high altitude.