FCC riser performance was examined in a large cold-riser model made of 0.186-m-ID plexiglass. In the prelift zone, distributions of particle velocity and local density in six cross sections were investigated, and the experimental results indicated that the whole prelift zone can be divided into three subzones in the axial direction. In the feedstock injection zone, some new flow parameters were introduced and five flow parameters in five different cross sections were measured. When a nozzle jet was injected, secondary flow of the jet exited in the vicinity of the riser wall due to vortices, and this flow moved forth, at first and then merged into the main stream. Based on the gas - solid two-phase flow characteristics in each zone, the whole feedstock injection zone of the riser can be divided-into four subzones. A new axial particle backmixing model and a simplified method for computing,the radial distribution of the nozzle jet concentration in a different riser cross section, can predict flow parameters of particles and the jet.