Abstract: By using the developed gas-particle two-phase flow-reaction model,the simulation of particle dynamicswas carried out in a commercial riser in FCC. The results show clearly that the catalysts backflow seriously in the nozzle zone by the influence of shoot and congregate in the pipe center. In the upper part of the riser reactor,catalysts flow in a fully developed steady current and the radial distribution of particle concentration gradually becomes what happens in vertical tubes,because the influence of shoot is more and more weakened. It is easy to find out that shoot influences the hydrodynamics of particle-phase intensively.