The invention discloses a device and method for measuring the reaction rate of a liquid alkali metal-water vapor interface. The device is characterized by comprising a vaporization mixing section, anoverheating section, a bypass section, an experiment section and a filtration measuring section. With visual shooting, the convection speed, the initial temperature and the water vapor concentration are controlled and the reaction time and the H2 concentration are measured, so that the reaction rate of the liquid alkali metal and the water vapor interface is obtained. According to the invention, aproblem that the reaction rate of the liquid alkali metal and water vapor interface cannot be measured under a high-temperature condition is solved based on the characteristics of turbulence reactionflow, so that reaction kinetic parameters of the turbulence two-phase interface are quantitatively studied.