Abstract: The detail flow structure and gas-solid contact efficiency in FCC riser were studied in a cycled fluidized bed cold model setup. Based on the gas and solid distributions, relative gas-solid contact efficiency (RCE) and cross-sectional average gas-solid contact efficiency (CCE) were defined. Results indicated that non-uniform axial and radial flow structures existed in riser, which were considered to be unfavorable to catalytic cracking reactions; RCE near the wall region of FCC riser was rather high and CCE decreased with the increase of riser height significantly.