Abstract: The paper discusses the experimental investigation on subsonic dif fuser. When in the front of the subsonic two-dimensional diffuser an elliptic bar is placed perpendicular to the flow stream and parallel to the diverging wall of the diffuser,the wake-type inlet velocity profile is created and the core-stream turbulence level at the entrance of the diffuser is increased, which results in flatter velocity profile implying an increase in momentum transport across the boundary layer.The value of the boundary layer shape factor is therefore decreased. Consequently,the flow separation is delayed and the separation range is reduced. As a result,the static and the total pressure recovery coefficients of the diffuser rise by 30% and by 3% respectively when the maximum Mach number of the diffuser inlet reaches 0.7.