The reaction characteristics of magnesiumbased hydroreactive fuel with water vapor were studied in the visual combustion device. The combustion reaction process of the fuel and vapor times were obtained from the highspeed charge coupled device (CCD) photographs. The combustion temperature was measured by thermal couple embed in the fuel. The reaction process of magnesiumbased hydroreactive fuel with vapor consists two steps(fast and slow reaction). The time and degree at the end of the fast fuelvapor reaction step are the key factors to characterize the reaction of the fuel and vapor. The reaction rate decreases with increasing of the reaction time and degree. The reaction rate and degree of the fuel with vapor can be increased by greater mass ratio of oxidizer to binder,higher content of fine magnesium powder,and ferrous additive. However,both the reaction rate and degree of the fuel with vapor decrease with higher content of magnesium powder. The fuel with the content of magnesium upward 60% should have greater mass ratio of oxidizer to binder and higher content of fine magnesium powder on the premise of assuring its energy properties,technical properties and mechanical properties.