NOVELTY - An internal-heating process for continuously preparing coal gas by pyrolyzing and gasifying biomass, comprises sending the biomass to a storage hopper of the pyrolysis-gasification furnace, moving the biomass from top to bottom in the furnace and conversely contacting with the crude pyrolyzed coal gas to exchange heat, drying and preheating the biomass, cooling the crude pyrolyzed coal gas at 70 degrees C after the heat exchange and exhausting the crude pyrolyzed coal gas at the outlet; and pyrolyzing and dry-distilling the biomass into the charcoal in the pyrolysis cylinder and transition cylinder.    USE - The internal-heating process is useful for continuously preparing coal gas by pyrolyzing and gasifying biomass (claimed).    ADVANTAGE - The process can continuously supply the biomass coal gas with high calorific value.    DETAILED DESCRIPTION - An internal-heating process for continuously preparing coal gas by pyrolyzing and gasifying biomass, comprises sending the biomass to a storage hopper of the pyrolysis-gasification furnace, moving the biomass from top to bottom in the furnace and conversely contacting with the crude pyrolyzed coal gas to exchange heat, drying and preheating the biomass, cooling the crude pyrolyzed coal gas at 70 degrees C after the heat exchange and exhausting the crude pyrolyzed coal gas at the outlet; pyrolyzing and dry-distilling the biomass into the charcoal in the pyrolysis cylinder and the transition cylinder through the heat generated by burning the recycled coal gas and the air at 600-800 degrees C, resolving the dry-distilled coal gas and sinking the pyrolyzed and dry-distilled charcoal into the gasifying cylinder through the pyrolysis cylinder and the transition cylinder; exhausting the crude pyrolyzed coal gas at the crude pyrolyzed coal gas outlet, entering the water-sealing dust collector to remove dust, entering the separated coal gas into a pneumatic trough, cooling in a spraying cooling tower and the pumping out with an exhaust fan, using one part of the purified coal gas to enter a combustion cabinet, using the other coal gas with the adjusted pressure as the recycled coal gas, entering the recycled coal gas into the transition cylinder of the pyrolysis-gasification furnace through the clean coal gas distributor, separating the oil-containing washing water separated out of the water-sealing dust collector and the spraying cooling tower in the tar distributor to remove the tar, and recycling the separated water; mixing and burning the recycled coal gas with adjusted pressure, entering the transition cylinder from the clean coal gas distributor, and the air in the air distributor, using the generated heat to heat the biomass in the transition cylinder at 600-800 degrees C; reacting the charcoal in the gasifying cylinder and the spraying cooling water, absorbing the heat, generating the water gas and the semi-water gas with calorific values of more than 8000 kJ/Nm3, raising the water gas and the semi-water gas and mixing with the dry-distilled coal gas to form the crude pyrolyzed coal gas, exhausting the coal gas from the crude pyrolyzed coal gas outlet, cooling the charcoal from 600-800 degrees C to 200 degrees C, cooling the charcoal at 50 degrees C through the water jacket of the cooling section of the gasifying cylinder, and discharging the charcoal at the charcoal outlet. An INDEPENDENT CLAIM is a pyrolysis-gasification furnace using the internal-heating process for continuously preparing coal gas by pyrolyzing and gasifying biomass, comprising a storage hopper, a furnace body, a pyrolysis cylinder, a transition cylinder and a gasifying cylinder, and a supporting leg; where the storage hopper is set on the furnace body; the furnace body from top to bottom is equipped with pyrolysis cylinder, transition cylinder, and gasifying cylinder; an air distributor is equipped between the pyrolysis cylinder and the transition cylinder; the pyrolysis cylinder is equipped with a crude pyrolyzed coal gas outlet; the cleaning coal gas distributor is equipped between the transition cylinder and the gasifying cylinder; the bottom of the gasifying cylinder is equipped with a charcoal outlet; the upper part is equipped with a cooling water sprayer; the lower part is a cooling section equipped with a water jacket; and the furnace body is set on the supporting leg.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of the pyrolysis-gasification furnace using the internal-heating process for continuously preparing coal gas by pyrolyzing and gasifying biomass.