To make the biomass tablets heated fully in a fluidized pyrolysis liquefaction process, it ought to be ensured that sufficient biomass granules stay long enough in the bed so as to meet or exceed the expected pyrolysis temperature. That is, the prerequisite is that the staying time must be more than or equal to the pyrolysis time. However, the staying time is decided by the flow speed and CFB parameters, and the pyrolysis time is controlled by the heat transfer process of biomass particles in a fluidized bed both of which are closely related to the parameters of biomass particles. This paper analyses the heat transfer process of the biomass in the pyrolysis reaction tower, establishes a simplified model of heat transfer with a gassolid flow, studies the rule of pyrolysis time and staying time changing with the biomass size and finds out a theoretical method of selecting the expected parameters of biomass granule to ensure the full pyrolysis of biomass materials.