The invention provides a method and a device for preparing biological oil by biomass cracking. Biomass material is prepared into the biological oil after being smashed, dried, thermally cracked, secondarily condensed and separated. The device mainly comprises a feeding system, a fluidized bed reactor, a heat carrier separator, a gas-solid separator, a heat carrier heating device, a condenser, and the like, wherein the heat carrier heating device is divided into two layers which are partitioned by a heat insulated board and evenly distributed with a plurality of ceramic heat pipes used as a heating carrier of a heat transfer element. The invention not only utilizes subsidiary product of thermal cracking, namely carbon and non-condensable gas as energy sources for thermal cracking liquification, but also effectively utilizes the smoke discharged by the heat carrier heating device as fluidizing gas, thereby having various advantages of reasonable process, no secondary pollution, energy saving, low cost, and the like. Compared with the prior art, the invention is easier to popularize and apply.