The invention discloses a method and a device for three-stage separating 
biomass gasification. The device mainly comprises a reacting furnace, a 
pyrolysis chamber which is a 
biomass pyrolytic 
reaction chamber is arranged on the upper portion of the reacting furnace, a gasification chamber and a 
combustion chamber are positioned in the reacting furnace, the gasification chamber is positioned inside the 
combustion chamber, the 
pyrolysis chamber and the gasification chamber are connected with a feeding 
pipe, a 
flue gas channel is arranged outside the 
pyrolysis chamber and the feeding 
pipe, a feeding device is arranged on the upper pyrolysis chamber, the lower gasification chamber is communicated with the 
combustion chamber, a high-temperature gas extraction outlet is arranged in the middle of the gasification chamber, 
flue gas rises up along the 
flue gas channel from the 
combustion chamber to the periphery of the pyrolysis chamber and then is exhausted via a 
flue gas outlet, and the exhausted high-temperature gas is separated and purified by a separator prior to entering an air pre-heater. Three processes of a 
biomass gasification generating 
system are completely separated, the length of a reduction area is increased, and time and temperature required by 
tar pyrolysis are guaranteed, so that content of 
tar in the gas is reduced, gas 
generation rate of the gasification furnace is increased, and quality of the biomass gas is improved. The device has the advantages of convenience for 
temperature control, energy saving, 
environmental protection, operating continuity and the like.