Abstract: The axial and radial distributions of the local particle velocities at different radial positions on various axial levels along the downer-column were measured by using a PV-4A fiber-optic particle velocity probe in a half-column downer of 2m high and 30mm I.D.,and the effects of operation conditions and spouted positions on the local particle velocities were also investigated in this paper. Then the radial particle velocity distributions of binary particle mixture，formed by respectively and simultaneously injecting fine-FCC catalysts and coarse-glass beads in downers，were examined at different composition ratios of FCC catalysts to glass beads. Finally, based on the concept of dimensionless local particle velocities the new correlations for predicting the local particle velocity distributions of FCC catalysts and glass beads were developed by regressing experimental data from literatures and this study. Results show that the radial distributions of local particle velocities vary significantly with the particle properties, and for binary particle mixture, the radial distributions are more uniform as compared with those of only FCC catalysts and the double-peaked distribution characteristics of particle velocity profiles become more obvious with the increase of superficial gas velocities, since in this case fine particles mixed by injecting coarse particles will result in the variation of gas-solids dynamic mechanism and the smoothness of particle velocity distributions in dowers.