The invention relates to an apparatus for detecting reactivity of alkali metal on coke and intensity influence after reaction, which belongs to the technical field of ironmaking experiment equipment. The apparatus is used for detecting influence of reactivity of blast furnace softening dropping band alkali metal vapour on coke and intensity influence after a reaction, a technical scheme is characterized in that a graphite crucible is placed at center of a furnace body, a silicon-molybdenum rod is arranged outside a corundum pipe at outer part of the graphite crucible, the silicon-molybdenum rod is connected with a temperature controlling device, a furnace temperature display instrument and a hearth temperature display instrument are arranged on the furnace body, and are connected with the temperature controlling device. The graphite crucible is divided into an upper layer and a lower layer, the upper layer is filled with a charging material, the lower layer is filled with solid potassium bicarbonate pellets, so that potassium steam can be continuously provided during an experiment process. The apparatus simulates an influence process of the reactivity of blast furnace softening dropping band alkali metal vapour on the coke and the intensity after the reaction, provides accurate technological parameter for production, and plays vital effect for guidance production.