NOVELTY - A biological oil comprises (wt.%): carbon (more than 71.1), hydrogen (more than 7.3), oxygen (more than 16.6), and nitrogen (more than 0.1), where oil has viscosity of more than 106 MPa-s, concentration of more than 1.10, pH value of more than 2.5, and water ratio of less than 20%.    USE - As biological oil.    ADVANTAGE - The biological oil comprises chemicals (phenol and aldehyde), thus having high economical value. The method utilizes quick thermal cracking middle temperature biomass stable fluidized bed reactor, is simple and has wide source of raw materials, and achieves 75% yield.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method for preparing the biological oil comprising:    (A) crushing and drying biomass until water ratio is less than 8% and then preparing bed material particles with less than 2 mm particle diameter;    (B) providing generated oxygen-lacking gas and then dividing gas coming out of the gas buffer tank, where bigger flow is preheated after entering reactor bottom and smaller flow is connected through material hopper top part;    (C) thermal cracking biomass particles at 5-10 kg/hour and then mixing oxygen-lacking gas with fluidized bed material;    (D) adding lanthanum-cerium rare-earth compound (1-3%) as catalyst and then heating at 450-550 degrees C;    (E) generating cracking steam and wood coal and then pyrogenating at 1-1.4 KPa, where wind speed of fluidization is 0.20-0.30 m/s;    (F) collecting wood coal and then collecting oil steam in cracking steam and then condensing at - 1-1 degrees C, where non-condensable gas in cracking steam is stored by compressed gas tank through filter;    (G) adding cobalt-molybdenum as catalyst at 9-11 MPa and 300-350 degrees C and then adding hydrogen for 3-5 minutes; and    (H) distilling at 380-450 degrees C to obtain the biological oil.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic block diagram illustrating a method for preparing the biological oil. (Drawing includes non-English language text).