An experimental study was conducted to characterize the effects of vitiate species (H2O and CO2) on supersonic combustion. These species were added to an initially clean airflow that was supplied by an electrically heated direct-connected facility. Wall pressures were measured by pressure sensors, combined with combustion optical images, and the influence of major vitiate species (H2O and CO2) on supersonic combustion was analyzed. Experimental results showed that the presence of vitiate species decreased combustor pressures by 3% to 30% for the same fuel equivalence ratio. The combustion flame images indicated that the flame-spreading angle decreased with the increase of the molar fraction of H2O and CO2, and when the molar fraction of CO2 was increased to 3.5%, an illogical oscillation, specifically embodying as the flame round switching between the upstream cavity and the downstream cavity, could be observed in the combustion, which might possibly cause the flame extinction.