Dispersed phase droplet behavior research is very important for the design and scaling up of extraction columns. Recently, the droplet velocities at high holdup were found to be uniform, which means the conventional concept of forward mixing needs correction. The drop size distribution only influences the mass transfer coefficients and not the residence time distribution of droplets. In this work, an improved dynamic combined model considering the influence of drop size distribution has been developed, by which the axial mixing can be easily evaluated using a one-dimension search. A typical experimental system of 30% tributyl phosphate (TBP) (in kerosene)-nitric acid-water with interfacial tension of 0.00995 N/m, was used to investigate the mass transfer performances in a coalescence-dispersion pulsed-sieve-plate extraction column (CDPSEC) with 150mm in diameter. The two-point dynamic method was used to obtain the stimulus-response curves. With these results, the axial mixing in the CDPSEC was evaluated. The calculated results showed that the response curves could be predicted by the dynamic combined model with a deviation less than 0.001. This model has marked advantages over previous models in literature because of its accuracy, simple boundary conditions, and single parameter optimization. (c) 2005 Elsevier Ltd. All rights reserved.