The invention discloses a device for measuring the thermal conductivity of a fireproof material at the high temperature. The device is characterized in that two low-temperature side core plates are arranged on the outer sides of two plate-shaped fireproof-material samples, the peripheries of a heating core plate, the periphery of the plate-shaped fireproof-material samples and the peripheries of the low-temperature side core plates are wrapped by heat insulating layers, heat conducting plates are located on the outer sides of the low-temperature side core plates, the heating core plate, the plate-shaped fireproof-material samples and the low-temperature side core plates are fastened into an integral structure through bolts, and then the integral structure is arranged in an electric furnace; a single-head heating rod in the heating core plate and single-head heating rods in the low-temperature side core plates are connected with a direct-current stable power source, and the direct-current stable power source is connected with a temperature regulator; thermocouples are connected with the temperature regulator, the temperature regulator is connected with a data acquisition instrument, and the data acquisition instrument is connected with a computer. According to the device, the thermal conductivity of the plate-shaped fireproof material such as a homogeneous material, a heterogeneous material and a multiplayer composite material in the direction of the whole thickness in the process from the room temperature to the high temperature of 800 DEG C can be measured.