NOVELTY - Preparing high-quality biological oil by selective pyrolysis of biomass comprises: (a) carrying out one-stage low temperature pyrolysis: conveying the biomass raw material that is pulverized to thin granules to a spiral pyrolysis reactor; (b) carrying out two-stage low temperature pyrolysis: conveying the pyrolysis residual coke to a shallow bed fluidized bed; (c) carrying out three-stage pyrolysis: guiding the pyrolysis solid product into the deep fluidized bed; and (d) generating high-temperature smoke gas: guiding the pyrolysis gas to a combustion chamber to be sufficiently combusted.    USE - The process and the device are useful for preparing high-quality biological oil by selective pyrolysis of biomass (all claimed).    ADVANTAGE - In utilizing the process and the device, the prepared biological oil has low content of water, acidic substance and solid granules, and good stability of storage and transportation.    DETAILED DESCRIPTION - Preparing high-quality biological oil by selective pyrolysis of biomass comprises: (a) carrying out one-stage low temperature pyrolysis: conveying the biomass raw material that is pulverized to thin granules to a spiral pyrolysis reactor, pyrolyzing at 200-280 degrees C to produce pyrolysis gas and pyrolysis residue of biomass, congealing and dewatering the gas to get the aldehydes and organic acid chemicals; (b) carrying out two-stage low temperature pyrolysis: conveying the pyrolysis residual coke to a shallow bed fluidized bed, fast pyrolyzing at 300-350 degrees C, controlling speed of air flow of the fluidized bed to be 0.1-0.5 m/second, producing pyrolysis gas containing micro-molecular phenols compound and pyrolysis solid product rich in cellulose and some lignin, separating gas and solid, congealing; (c) carrying out three-stage pyrolysis: guiding the pyrolysis solid product into the deep fluidized bed, fast pyrolyzing at 450-600 degrees C, controlling speed of air flow of the deep bed fluidized bed to be 0.2-0.8 m/second, filtering solid granules in the pyrolysis gas by a bundling filter and guiding the filtered pyrolysis gas to a tubular heat exchanger, congealing the congealable gas in the pyrolysis gas to get the high-quality fuel, collecting the fuel in a biological oil collecting tank; and (d) generating high-temperature smoke gas: guiding the pyrolysis gas to a combustion chamber to be sufficiently combusted to produce high-temperature smoke gas, de-ashing and purifying the smoke gas; conveying one part to outer heating gas inlet of the spiral pyrolysis reactor to be used as the pyrolysis heat source; and conveying the other part of the smoke gas to the smoke gas inlets of the shallow bed fluidized bed and the deep bed fluidized bed to be respectively used as the pyrolysis heat source and the fluidized gas. An INDEPENDENT CLAIM is a device for preparing the high-quality biological oil by selective pyrolysis of biomass comprising a spiral pyrolysis reactor (1), a shallow bed fluidized bed (2), a deep bed fluidized bed (3), a combustion chamber (4), a condensing tower (5), a tubular heat exchanger (6), and a biological oil collecting tank (7); where the spiral pyrolysis reactor is used for pyrolyzing the biomass raw material at low temperature; a feeding funnel (11) is set at the front end of the reactor; a pyrolysis gas outlet (1-1) and a pyrolysis residual coke outlet (1-2) are set at the rear end of the reactor; a spiral propelling shaft (9) is provided in the reactor; a heating cover (10) is provided at the outer part of the reactor; a spiral propelling shaft (9) is of increasing expanding structure; the shallow bed fluidized bed is used for further fast pyrolyzing the pyrolysis residual coke produced by the spiral pyrolysis reactor; the pyrolysis residual coke outlet of the spiral pyrolysis reactor is connected to the feeding hole of the shallow bed fluidized bed through a first star-shaped discharging valve (16) and a first spiral feeder (17); a high temperature smoke gas inlet (20) is set under the shallow bed fluidized bed; a solid product outlet (22) is set at the middle lower part of the shallow bed fluidized bed; a cyclone separator (18) is set at the middle upper part of the shallow bed fluidized bed; a congealing liquid output port (5-1) and a non-congealed gas outlet (5-2) are provided at lower part of the condensing tower; the deep bed fluidized bed is used for fast pyrolyzing the pyrolysis solid product produced by the shallow bed fluidized bed again; the solid product outlet of the shallow bed fluidized bed is connected to the feeding hole of the deep bed fluidized bed through a second star-shaped discharging valve (23) and a second spiral feeder (24); a high temperature smoke gas inlet (25) is set at lower part of the deep bed fluidized bed; a bundling filter (6-1) is set at the middle part of the deep bed fluidized bed; a gas outlet (26) is set at the upper part of the deep bed fluidized bed; the output side of the bundling filter is connected to the input end of the tubular heat exchanger; a non-congealed gas output pipeline (6-2) and a congealing liquid output pipeline are provided at lower part of the tubular heat exchanger; the combustion chamber comprises a fuel input port, an air input port (27), and a high temperature smoke gas output port (28); and the high temperature smoke gas can be output from the high temperature smoke gas outlet after being purified by the cyclone separator (4-1).    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of the device for preparing high-quality biological oil by selective pyrolysis of biomass.    Spiral pyrolysis reactor (1)    Pyrolysis gas outlet (1-1)    Pyrolysis residual coke outlet (1-2)    Shallow bed fluidized bed (2)    Deep bed fluidized bed (3)    Combustion chamber (4)    Cyclone separator (4-1,18)    Condensing tower (5)    Congealing liquid output port (5-1)    Non-congealed gas outlet (5-2)    Tubular heat exchanger (6)    Bundling filter (6-1)    Non-congealed gas output pipeline (6-2)    Biological oil collecting tank (7)    Spiral propelling shaft (9)    Heating cover (10)    Feeding funnel (11)    First star-shaped discharging valve (16)    First spiral feede (17)    High temperature smoke gas inlet (20)    Solid product outlet (22)    Second star-shaped discharging valve (23)    Second spiral feeder (24)    High temperature smoke gas inlet (25)    Gas outlet (26)    Air input port (27)    High temperature smoke gas output port (28)