A stimulus-response technique was used to determine the residence time distribution (RTD) of liquid phase in the gas-liquid-solid mini-fluidized bed with 3 mm bed diameter. Deionized water and air were used as liquid phase and gas phase

respectively. Glass beads and alumina particles with the mean particle size of 0.123-0.222 mm were taken as solid phase. KCl tracer as an input signal was injected into the fluidized bed through a sample injector. The RTD of liquid phase was obtained by analyzing the conductivity at the bed outlet. The results indicate that the RTD become significantly smaller with the increase of superficial liquid and gas velocities. The mean residence time increases at lower superficial liquid and gas velocity or with the addition of solid particles. The flow is close to laminar flow when the superficial liquid velocity is set at 1.96-15.70 mm×s-1

meanwhile superficial gas velocity 1.18-1.96 mm×s-1. The mean residence time of liquid phase in the gas-liquid-solid mini-fluidized bed is (19.6±0.34) s-(48.0±0.92) s. A correlation of the Peclet number is able to predict the experimental data within a relative deviation of ±25%. The research results have guiding significance for the design amplification of small three-phase fluidized bed.