An experimental study of a rectangular cross section scramjet combustor was carried out.The effects on mixing and combustion performances of the rearward-facing steps,fuel injection orifice arrangements and the length of the constant height section downstream of the step were examined.The peak wall pressure,namely the strength of the precombustion shock,increased as the length of the constant height secthe constant height section must be selected so that it gives the most suitable strength of the precombustion shock갋Sweep of the rearward-facing steps and the orifice arrangements had little effect on the mixing and combustion efficiencies.