The spatial-developing flat-plate boundary layer of Mach number of 6 was simulated. The influences of the two-dimensional transverse micro-cavities on the base flow and the second mode instability wave were studied by adding them on the flat-plate surface. Results indicated that the two-dimensional micro-cavity configuration had a larger size (more than 100 μm) compared with the conventional porous coating. The comparison of the base flows showed that the micro-cavities had little effect on the streamwise velocity. No new instability mode appeared on the spectrum of the sampling point. The micro-cavities could be helpful to reduce the frictional drag. The drag caused by the pressure difference in the cavities was one to two orders of magnitude lower than the frictional drag. As the porosity increased

the total drag decreased. A reduction over 40% on the total drag can be reached when the porosity was 06. Two ways were employed for adding second mode instability waves at the inflow boundary

including a single-mode disturbance and a superposition of multi-modes disturbances. The downstream evolution indicated that the transverse micro-cavities had apparent suppression effect on the amplification of the second mode within a broadband frequency range

and the control effect became stronger with the increasing porosity.