Effects of design parameters on fuel-jet / airflow mixing in presence of pseudo-shock system were experimentally investigated. The fuel-jet was simulated by inert helium injection, and the pseudo-shock wave system was generated in a duct by backpressurizing Mach 2.5 airflow with a mechanical valve. Cross-sectional aspect ratio of the duct, injection conditions such as orifice diameter and injection pressure, and pseudo-shock wave location with respect to the injector location were varied. Crosssectional aspect ratio had sizable effects on mixing characteristics through interaction of injectant plume with wall and/or boundary (i.e., neighboring jet). Injectant mass flow rate was dominant among other injection parameters, and a length scale taking mass flow rate into account was found to be effective to summarize mixing data. Location of the pseudo-shock wave system had sizable effects on mixing characteristics even the shock train itself was terminated at the injector location, and better mixing was attained for closer location.