A spout-fluid bed with a draft tube is one modification of a conventional spouted bed. Here, a 100 mm diameter semi-cylindrical spout-fluid bed with a 14 mm diameter draft tube was used to investigate the effects of flow rates of spouting gas from the central nozzle and auxiliary gas from the conical base distributor and the length of the entrainment zone on the behavior of gas and solid particles in the bed. CO(2) traces were employed to examine gas bypassing characteristics. Flow patterns of solids can be classified into five flow regimes according to the spouting gas flow rate and the auxiliary gas flow rate. Although the minimum spouting gas velocity decreases with increasing auxiliary gas flow rate, the minimum total gas flow rate for operating a stable spouting mode increases. Gas flow rate through the annulus and solids circulation rate are enhanced when the auxiliary gas flow rate increases or the entrainment zone is extended. Moreover, it was recognized that the gas bypassing flow rate remarkably affects the solids circulation rate.