Abstract: An experiment has been performed to investigate the control separation of turbulent boundary layers in subsonic diffuser using a transverse cylindrical turbulization device to modify the boundary layer structure.Results of the study indicated, that the transverse cylindrical turbulization device will give substantial depression of boundary layer separation. The mechanism of turbulization device is due to change of flow monentum near the wall of diffuser.In this paper the measuring results of turbulance distribution in boundary layers were also discussed.