The residence time distribution (RTD) curves were measured to observe the shell-side flow status in hollow fiber modules (HFMs) with different packing densities, and with 30%TBP in kerosene/phenol/water as experimental system, the membrane extraction was carried out in three polypropylene HFMs in counter-current flow. A random distribution model described by the Voronoi tessellation method based on normal distribution function was proposed to determine the effect of random packing on the flowstatus and mass transfer characteristics. The standard deviation in normal distribution function represented the packing irregularity in commercial HFMs. So the random distribution model related the packing irregularity with the flow status and mass transfer performance in random packing modules. The theoretical calculation and experimental results indicated that the random packing of fibers caused the non-ideal flow and significant decrease in mass transfer performance; furthermore, the non-ideal flow in shell side had an influence not only on the mass transfer performance in shell side but also on that in lumen side.