Abstract: The new 1.2 m high speed wind tunnel of China Aerodynamics Research and Development Center (CARDC) is an intermittent subsonic, transonic and supersonic wind tunnel in which the dynamic pressure is adjustable. It adopts innovative design solutions such as a horizontal semi-return aerodynamic layout, dual-ejector drive system, nozzle-test section integrated design, and flap secondary throat configuration. Through performance adjustment and calibration, the commissioning of four independent operating modes was completed, meeting the simulation requirements of different types of test. Though the adjustment and optimization of control algorithms and strategies, high control accuracy for both total pressure and Mach number has been achieved, as well as a wide dynamic pressure envelope and Mach number range. The optimization and calibration of processes have enhanced the flow field quality. The results indicate that the instability of total pressure and Mach number is better than 0.2% and 0.002 respectively, and the flow field uniformity meets the advanced standard. The overall performance of the wind tunnel has fully achieved the design specifications.