The axial profiles of cross-sectional average solids holdup profiles were studied in two 10 m long, 76 mm i. d. and 203 mm i. d. risers with the solids circulation rate up to 550 kg/m2s, superficial gas velocities up to 10.0 m/s, and solids inventory up to 410 kg in the 320 mm i. d. storage tank. The shape of the axial profiles of the cross-sectional average solids holdup changes with solids fluxes. Under high-flux conditions, the shapes of the profiles are quite different from those under low-flux conditions. It is clear that solids holdup increases with the increase of solids fluxes. While the superficial gas velocities have no obvious influence on the shape of the axial profiles of the cross-sectional average solids holdup under given solids flux for both risers, solids holdup decreases with the increase of superficial gas velocity under all solids inventories. The solids inventory and riser diameter have little influence on the shape of the profile, but the solids holdup is higher with larger bed diameter and/or larger solids inventory. Meanwhile, the solids inventory and riser diameter have important influence on the maximum value of operating solids fluxes of the system. The maximum of solids fluxes increases with the increase of solids inventory, and decreases with the increase of riser diameter.