Abstract: A new mathematical model for the gas and solid phases Catalyzed Acrylonitrile (AN) fluidized bed reactor using V-Sb-Al catalyst is presented in this study. This mathematical model accounts for mass and heat transfer between gas and solid phases with chemical reaction that occurs at the surface of the catalyst particles. The proposed mathematical model evaluates the effect of catalyst flow rate and superficial gas velocity on the system. Concentration and temperature profile changes are also estimated. Moreover, the results of the proposed model are compared with experimental data in terms of concentration and temperature reaction. Obtained results shows good agreement with the actual plant data.