Abstract: Fluid catalytic cracking (FCC) process is one of the most important heavy oil upgrading techniques in the petroleum refining industry,and riser reactor is the crucial part in FCC unit. The experiment was conducted in a big cold riser model made of plexiglass with cross-section 0.186m in ID and height 14m.The operating conditions were decided according to industrial practice.The solid particle was a type of FCC cracking catalyst while the gas entering the riser via the nozzles and via the pre-lift zone is air. Particle velocity,local density,particle backmixing ratio,concentration of jet fluid in five different cross-sections were measured.The radial distributions of these parameters show that when nozzle jet is injected into,a secondary flow of jet fluid comes forth in the vicinity of the riser wall due to vortices regime,this secondary flow expands at first and then merges in the main stream. The whole feed injection zone of riser could be divided into four zones according to gas-solid two-phase flow characteristics in each zone.Moreover,these four zones could also be divided into two or three regions.