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In this paper, a novel experimental investigation was conducted to enhance the combustion of boron-containing fuel-rich mixture by steam reforming in a supersonic flow. The ground direct-connected experiments were designed to simulate a flight condition at Mach number 5.9 and an altitude of 25 km. The operating characteristics and performance evaluation of the scramjet combustor were analyzed and discussed. The experimental results demonstrate that steam reforming can enhance the combustion of boron-containing fuel-rich mixtures in the supersonic flow. The performance of the combustor is firstly enhanced and then weakened with the increase of the steam-fuel ratio. The optimal steam-fuel ratio is approximately 0.189, which maximizes performance. At this steam-fuel ratio, combustion efficiency reaches 0.451, which is 9.9 % and 7.4 % higher than steam-fuel ratios of 0 and 0.395, respectively. The possible mechanism of steam reforming promoting boron combustion in the supersonic mainstream is explained. Steam accelerates the removal of the liquid oxide layer surrounding the boron particle, then combines with oxygen to produce hydrogen with good ignition-combustion characteristics and a new oxide layer. The cycle continues until the boron burns out. These conclusions can promote an understanding of enhancing the combustion of boron-containing fuel-rich mixture by steam reforming in the supersonic flow. [ABSTRACT FROM AUTHOR]