Abstract The effects of micro-ramp on the characteristics of transverse jet were investigated by the LES simulation at Mach 2.7, with recycling-rescaling method applied to reproduce the turbulent boundary layer. The transverse nitrogen jet in front of micro-ramp and behind micro-ramp were studied by comparison with plate jet. It is found that the micro-ramp can improve the penetration height obviously, while placing jet orifice behind micro-ramp, due to the low freestream momentum in ramp wake. On the other hand, when placing the jet orifice in front of micro-ramp, the improvement in penetration is quite slight, because most injection is above the boundary layer and micro-ramp has little influence on the main flow. It is also observed that unlike the periodic Kevin Helmholtz (K–H) vortices appeared in ramp wake, the periodic K–H vortices are not achieved in jet cases.