The invention relates to a biomass carbonization furnace which comprises a carbonization chamber; a pyrolysis chamber is arranged at the lower part in the carbonization chamber, a combustion chamber is arranged at the upper part in the carbonization chamber; the pyrolysis chamber and the combustion chamber are communicated with each other; a feeding port and a discharging port are respectively formed in two ends of the pyrolysis chamber along the length direction; a feeding screw conveyor is arranged in the pyrolysis chamber, and a screw shaft of the feeding screw conveyor can convey materialsat the feeding port to the discharging port and stir materials in the pyrolysis chamber; the pyrolysis chamber is provided with a lower air supply port, the combustion chamber is provided with an upper air supply port, and the lower air supply port enables air to enter the pyrolysis chamber. According to the invention, the output of pyrolysis gas is controlled through the gas supply amount of thelower pyrolysis chamber; pyrolysis gas generated after material carbonization rises to the upper combustion chamber to be combusted, meanwhile, heat radiation generated by combustion is fed back to material pyrolysis, heat radiation is provided for the pyrolysis process, carbonization is achieved in cooperation with material combustion, the material carbonization quality is improved, and materialcarbonization is uniformized through stirring.