Abstract: In order to study the agglomeration mechanism, the gas-solid flow field in the deposition chamber was numerically studied by Euler-Euler method, and the steady-state reduction reaction products were simulated by HSC Chemistry. Combined the flow field distribution and reduction reaction simulation, the velocity and component concentration fields in the deposition chamber were obtained. The results showed that both the gas-solid flow fields and reaction products concentration fields in the deposition chamber were not uniform, and local particle accumulation phenomenon in deposition chamber cone section was found. The bed agglomeration can be attributed to the melting of the low valence niobium chloride produced by reduction reaction. The reaction rate and NbCl₅ flow non-uniformity can lead to the low valence niobium chloride generation increases significantly, which can promote the bed agglomeration.