Biomass fast pyrolysis technology is one of most promising methods to utilize biomass resources, for its high production of pyrolysis liquid named bio-oil. And the fast pyrolysis fluidized reactor is widely used because of the advantages of simple structure, and easy to enlarge. The understanding of computational fluid dynamics (CFD) of its fluidized bed is necessary basis for particulate heat transfer and pyrolysis kinetics research. In this paper, modern hydrodynamic theory and calculation means is employed to simulate the cold state of fluid behavior in the pilot-scale fluidized pyrolysis reactor. The simulation results are in good agreement with the empirical equation and experimental data, with resultant error lower than 10%. Based on the cold state simulation, we modeled the fluid flow behavior in the fluidized reactor during fast pyrolysis under high temperature, and calculated the fluidization velocity and the distribution of solid phase fraction.