A high-pressure combustor and a metal/steam reactor were used to simulate the two-stage combustion of a fuel-rich propellant used for water ramjet engines. The solid combustion products from the two stages were collected and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). In addition, the thermal properties of the solid products of the primary combustion were characterized by differential thermal analysis (DTA) and simultaneous thermogravimetry (TG). The burning rates at different pressures were measured and the secondary combustion process in hot steam was monitored by high-speed cinematography. The results showed that the propellant has a good combustion performance and a high burning rate. After primary combustion, the solid product mainly contained magnesium, magnesia, magnesium chloride, and carbon. During the secondary combustion, the ignition temperature was approximately 720?degrees C, and two burning stages were observed. The rest of magnesium hasnt completely reacted with hot steam until the temperature reached a value higher than 800?degrees C for 30 min.