Experiments on maldistribution were conducted in a 8.5 m high, 1 m×0.3 m cross-section circulating fluidized bed equipped with a 33 bubble-cap distributor. There exists an uneven distribution in flow rate, the bubble caps in the center region having larger flow rates than those next to the wall. Flow resistance has been found to be the dominating factor influencing gas flow rate distribution. Increasing superficial gas velocity improves flow rate distribution for a low pressure-drop distributor. For a high pressure-drop distributor, superficial gas velocity has little effect on flow rate distribution. A ratio of maximum flow rate through a bubble cap to average flow rate through all bubble caps (Vmax/Vav) characterizes the flow rate distribution. Distributor-to-bed pressure drop ratio (ΔPd/ΔPr) is another necessary parameter to achieve even flow distribution. A correlation between these two ratios is developed for predicting flow rate maldistribution in CFB bubble-cap distributor.