Wind tunnel experiments show that plasma generated by on-board discharges can be implemented to for significant mitigation of shock waves generated in front of a 30° half-angle truncated-cone model placed in a Mach 2.5 flow. Experimental evidences establishing two criterions that plasma has to be generated in the region upstream of the baseline shock front and has to have a symmetrical spatial distribution with respect to the axis of the model, in order to have significant effect on shock waves, are presented. Experimental results also exclude the thermal effect as a possible cause of the observed shock wave mitigation. A physical mechanism of the observed nonthermal plasma effect on shock waves is presented. Analysis shows that a symmetrically distributed plasma spike in front of the shock can effectively deflect the incoming flow symmetrically. The required electron density and energy of the plasma spike are calculated, whose values are within the experimental ranges.