The effect of temperature on solids mixing rate was investigated quantitatively by measuring the residence time distribution （TRD） in a co-current gas-solid fluidized bed. The variables selected for this investigation were temperature, gas flow rate and aspect ratio which is ratio of the bed height to diameter. The experimental results showed that the onset of fluidization occurred earlier than the expected velocity as the temperature rise. The results also showed that the gas flow rate and aspect ratio had a marked effect on the mixing pattern of solids, but temperature elevation increased the mixing effect slightly.