Mathematical models have been used to evaluate the relative importance of bubble rising with coalescence, mixing of particles in the dense phase, chemical reaction bubble cloud, and diffusion between bubble and dense phase of gas fluidized catalyst bed, over a certain range of operating conditions. The comparison between the models and kinetic data of isomerization reaction of n-Butene（Namkoong et al.） shows that the fluid in the dense phase is well mixed and the rate of reaction in the bubble cloud is small compared to the rate of convective exchange between two phases.