The axial apparent solids holdup and flow development is studied in two riser circulating fluidized bed reactors of different heights (10 m and 15.1 m risers), but similar diameter (76 mm and 100 mm). Pressure transducers were used for the measurement of axial solids distribution and flow development. For a higher riser, the axial distribution of solids holdup becomes more uniform along the riser. The apparent solids holdup increases with the increase of solids circulating rate or decrease of superficial gas velocity. However, the influence of these operating conditions on solids holdups at different axial regions have different tendency of change, which is quite different at particle acceleration region and fully developed region. A more accurate correlation is proposed to predict average solids holdup at a fully developed region of CFB riser.