The invention relates to a method and device for burning coal slime in a fluidized bed boiler. When the coal slime is burned in a medium and small-capacity circulating fluidized bed boiler, the way of feeding at the top of a furnace chamber is adopted; as the feeding point of the coal slime is near to the outlet of the furnace chamber, a large amount of the coal slime can fly out of the furnace chamber under the situation that the coal slime is not burned completely, and the burning efficiency is very low. The invention discloses the method for burning the coal slime in the circulating fluidized bed boiler, and the technical process of the method is as follows: sending the pasty coal slime into a dense phase region at the lower part of the furnace chamber of the circulating fluidized bed boiler, utilizing a device for burning the coal slime in the circulating fluidized bed boiler to smash the falling coal slime into small particles and disseminate the particles into the furnace chamber, mixing the coal slime with ascending smoke gas and recyclable materials, and then burning in the furnace chamber. The method and the device are used for burning the coal slime in the circulating fluidized bed boiler.