A novel, self-heating biomass fast pyrolysis reactor named internally interconnected fluidized beds (IIFB) was proposed for the efficient production of bio-oils and chemicals by catalytic fast pyrolysis of biomass. The IIFB reactor mainly consisted of a pyrolysis bed (biomass pyrolysis) and a combustion bed (char burning and catalyst regeneration) connecting through a draft tube and a dipleg. Each bed was designed for the continuous operation. The hydrodynamic characteristics of the reactor, such as solid circulation rate, pressure distribution, and volume fraction of particles were performed using numerical simulation in this study. A non-steady-state, Eulerian multi-fluid model was used. The gas phase is modeled with a k-epsilon turbulent model, and the particle phase is modeled with the kinetic theory of granular flow. The experiments were carried out in an IIFB experimental system to verify the model. The simulation results show that the solid circulation rate was kept as a constant of 110 kg/h after 12 s of computational time compared to the value of 104.5 kg/h obtained in the experiments. The time-averaged values of the pressures at different positions after 12 s of computational time were also close to the experimental data. The particles in the dipleg were monitored to drop downward at a uniform speed of 0.07 m/s. In comparison to that in the draft tube, the velocity magnitude (including vertical or horizontal directions) of the particles decreased along the height of the draft tube, whereas the vertical velocity of the particles first underwent a disturbed flow because of the solid solid and solid wall collisions, then increased rapidly, and last were kept at an almost uniform magnitude. The results can provide a conceptual guide for designing, building, and operating the system of biomass (catalytic) fast pyrolysis.