The effect of flow direction on hydrodynamics and mixing in the upflow and downflow circulating fluidized beds is discussed in details. Similar profiles of gas and solids velocities and solids concentration are found in both risers and downers. When the flow is in the direction of gravity (downer), the radial profiles of gas and particle velocity are more uniform than that in the riser, the solids mixing is very small and the flow pattern approaches plug flow, while the flow is against gravity(riser), the solids backmixing significantly increase and the flow pattern is far from plug flow. Among many of factors the now direction has the largest influence on hydrodynamics and axial mixing of gas and solids.