The main objective of this work is to analyse the effect of the particle phase stress model on the accuracy of prediction of the fluid dynamic of Circulating Fluidized Bed (CFB) Reactors. The fluid dynamic prediction of CFB is fundamental in its development and optimisation. In this work a two-dimensional hydrodynamic model for gas-particle flow has been used to compute the porosity, the pressure, and the velocity fields of both phases in 2-D axisymmetrical cylindrical co-ordinates. The fluid dynamic model is based on the two fluid model approach in which both phases are considered to be continuous and fully interpenetrating. CFB processes are essentially turbulent. The k-epsilon turbulence model, modified to consider the presence of the particle phase, was used to calculate the effective viscosity of the gas phase. For the particle phase inviscid model, Newtonian fluid with experimentally obtained viscosity constant and viscosity which was calculated from emerging kinetic theory of granular flows (KTGF) have been used to simulate the fluid dynamic of the CFB reactors. The results are compared with experimental data available in the literature.