The invention relates to a system and a method for pyrolyzing coal. The system comprises a pyrolyzing furnace and a rotary dust remover, wherein the pyrolyzing furnace comprises a raw material inlet, a semi-coke product outlet and a raw coal gas outlet; the rotary dust remover comprises a dust-containing gas inlet, a dust-free gas outlet, a blowback gas inlet and a dust outlet; the dust-containing gas inlet is connected with the raw coal gas outlet. Through the system and the method for pyrolyzing the coal, the separation of raw coal gas from semi-coke powder is achieved under the condition that the temperature is not reduced; the quality of subsequently prepared tar can be greatly improved; the separation of liquid tar from the semi-coke powder after the tar is cooled is avoided.