The invention relates to an environmental-friendly device of an iron and steel enterprise and a dust removal method, that is to say, a system and a method for treating converter flue gas. The system comprises a furnace mouth nitrogen injection sealing petticoat pipe, a segmental evaporation cooling flue, a high-temperature heat pipe steam generator, a spray evaporation cooler, a long neck adjustable throat venturi tube, an impeller type composite dehydrator, a fan, an automatic continuous coal gas detector and a three-way switching valve, which are connected in sequence, wherein the three-way switching valve is connected with a gas chamber; or the three-way switching valve is communicated with a chimney. The method comprises the following steps of: forming a soft sealing screen between a furnace mouth and a petticoat pipe, after segmentally vaporizing and cooling the flue gas, and cooling in a high-temperature heat pipe; after carrying out spray evaporation, cooling and rough dust removal through a dry method, carrying out fine dust removal and cooling by a venturi tube through a wet method, dehydrating the flue gas, and entering into a coal gas recycling stage lastly. According to the invention, the wet method and the dry method are combined, waste heat recovery, coal gas recovery, sewage treatment and dust removal can be planned in a flue gas treatment and utilization system as a whole and the combination action of the device is fully exerted.