The invention relates to a method for treating fine slag of a coal gasification device, and the method is used for recycling the fine slag of the coal gasification device. According to the method, after being dehydrated, slag slurry of a settling tank in the coal gasification device is made into slurry proper in concentration and pH value; specially-made flotation reagent prepared from ferric chloride, short-chain alcohol and M-oil according to the characteristics of the fine slag of the coal gasification device is added; flotation operation is conducted in a flotation machine, and thus flotation matter high in carbon content and tail ash high in ash content are obtained; the flotation matter and the tail ash are dried separately, so that refined carbon powder and tailings are obtained; and various products are further made according to customer requirements. In this way, resource utilization of the fine slag is achieved.