Abstract: Diffuser is the critical part of the hypersonic wind tunnel,The mainly role of the diffuser is to increase the static pressure at the diffuser exit.The wall static pressures and near-wall total pressure pressures along the diffuser are measured,and a measurement rake is installed to measure the flow parameters at the exit of diffuser and evaluate the internal flow performance of the diffuser.The results indicate that the phenomenon of“speed slow-up-slow-up”in inflow of the diffuser appears,the existing diffuser can ensure normal start of the wind tunnel and isolate the test section from disturbance of back pressure;the efficiency of the diffuser is correspond to the similar ones of foreign countries.If the stilling chamber pressure is lower,the diffuser has better effect of reducing speed and boosting pressure;conversely,the effect is not well,the Mach number at the exit is higher.