Gas-solids flow structures between a circular fluidized bed and a square fluidized bed were compared by differential pressure drops and solids holdups. The flow regime transition from bubbling to turbulent fluidization in the fluidized bed was studied by the standard deviations of pressure drop and solids holdup. The geometry effect on the regime transition was also discussed by comparing the local solids holdup profiles and instantaneous solids holdup signals between the circular and square beds. The frequency and duration time of the changeover between the dilute and dense phases around the transition progress were also studied by statistically analyzing the solids holdup signals in both the square and circular beds. (C) 2020 Elsevier B.V. All rights reserved.