The invention relates to a furnace body assembly of a coal gas producer; the furnace body assembly comprises a furnace body which is fixed and supported by a supporting mechanism; a coal gas outlet is arranged on the furnace body; a charging bucket is arranged at the top of the furnace body; a slag hole is arranged at the bottom of the furnace body; the furnace body assembly is characterized in that the furnace body comprises a water jacket, a furnace top and a lower furnace shaft, wherein the water jacket is filled with water, the furnace top is fixed at the upper end of the water jacket, and the charging bucket is arranged in the center of the furnace top; a coal gas outlet is arranged at one side of the upper part of the water jacket, and the lower furnace shaft is fixed at the lower end of the water jacket. The furnace body assembly has ingenuous and reasonable structure; as the water jacket is filled with water, the risk that the furnace body is burned up and burned through does not exists either under the condition that a hearth refractory brick falls off or has poor sealing performance, and therefore, the furnace body assembly has long service life and good safety performance; in addition, water in the water jacket can be heated to form water steam, and then the water steam is mixed with air to form a gasifying agent; and a device for supplying water steam does not to be additionally provided, thereby the device cost is saved.