A slag processing apparatus for superfine powder grinding industrial waste slag in an energy-saving and environmental-friendly type of closed cycle with high yield, the slag processing apparatus comprising a cracking device, a metering device for input material, a sprayer of grinded coal powder, a flame sprayer, a mixing combustion chamber, a lifting device, a powder screening device, a deduster, a wind guiding device, a storing tank for finished product, a wind sweeping-drying powder grinder, an automatic control device, two particle size detectors installed at an output port of the wind sweeping-drying powder grinder and a fine powder output port of the powder screening device respectively, and connected with the automatic control device which in turn is connected with the metering device for input material, the powder screening device, and the deduster.