Abstract: A riser with high density has unique behavior as compared with conventional circulating fluidized bed. With increase of cross-sectional solids fraction, the radial profiles of solids fraction,and particle velocity become significantly non-uniform. The objective of this paper is to develop unique internals that can improve the poor distribution of solids fraction and particle velocity. The experiments are conducted at a high-density riser with 0.186 m ID and 9.0 m in height. FCC particle with particle density 1398 kg·m -3 and average particle size of 54 μm as fluidized material. The apparatus was operated under typical conditions of high-density riser. Two-dimensional LDV and optical fiber density sensor are used to measure the particle velocity and solids concentration in the high-density riser. The radial solids concentration profile in the high-density riser is significantly changed with internals added in the riser. The solids concentration profile downstream the bluffs is much flatter than without internals case. The particle measurement shows that the core-annular structure is destroyed. Transient signal analysis shows that the particle turbulent intensity increases several times near the wall region. The addition of internals reduces the average solids concentration near the internals, while the solids circulating rate changes insignificantly with the addition of internals. The internals can make the radial solids concentration and particle velocity profile uniform downstream the riser, but the length that shows improvement of gas-solids flow in the riser by the internals is about 0.8 m.