Flow separation and recirculation resulted from a sudden constriction in the flow geometry,in the form of a forward-facing step (FFS),play an important role in both fundamental fluid dynamics research and many practical applications.[1-8] The flow over an FFS immersed in the turbulent layer produces complex flow structures due to the presence of two regions of separation and the local dynamic mechanisms remain largely unclear.[7] Owing to the compressible effects in supersonic flow,[9,10] the supersonic flow past the FFS immersed in the turbulent layer could produce more complex structures and need to be studied.Micro-vortex generators (MVGs) have attracted widespread attention in recent years for their promising utility in delaying shock-induced turbulent boundary layer separation.[11-21] The micro-ramp is one kind of MVG.In the present work,the nano-tracer planar laser scattering technique (NPLS) and particle image velocimetry (PIV) are employed to experimentally investigate the control effect of micro-ramps on flow over an FFS.