NOVELTY - The device has an exhaust branch pipe (21) connected to a spiral tube (7) in a biomass gasification furnace, and provided with a split flow exhaust control valve (20). A biomass gasification furnace is internally provided with a filter chamber (4) and a catalytic pyrolysis chamber (5). An outlet of the biomass gasification furnace is connected to a recuperative heat exchanger (11). The spiral tube is connected in the biomass gasification furnace and closer to a wall surface of an inner cylinder of the biomass gasification furnace.    USE - Device for heating down-draft biomass gasification furnace by engine exhaust.    ADVANTAGE - The spiral tube is partially installed in the gasification furnace, so as to heat the material in the gasification furnace, thus improving biomass gasification temperature and temperature of a catalytic pyrolysis chamber in the furnace. The heat exchanger is mounted on an outlet of the gasification furnace that supplies self-produced water vapor for the gasification furnace and condensates and cools the gas, so as to achieve water vapor and air as gasification agent. The device is simple in structure, low in flow resistance and easy to implement, and a down-draft biomass gasification furnace takes air as gasification agent, so that the gas heat value is improved by 20 percentage. The down-draft biomass gasification furnace and the catalytic pyrolysis of tar in the furnace are integrally combined to avoid the purification of tar in the gas, so that the content of tar is reduced by more than 60 percentage.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a method for heating down-draft biomass gasification furnace by engine exhaust.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a device for heating down-draft biomass gasification furnace by engine exhaust.    Filter chamber (4)    Catalytic pyrolysis chamber (5)    Spiral tube (7)    Recuperative heat exchanger (11)    Split flow exhaust control valve (20)    Exhaust branch pipe (21)