Shell side flow distribution in a randomly packed hollow fiber module was analyzed using the random cell model. The module was divided into subchannels. The hydrodynamics in each channel was described according to Happel's free surface model and then it was just the function of the local cell packing fraction. Based on the theoretical probability density distribution function of local packing fraction, the shell side flow distribution was presented. The results showed that a serious flow mal-distribution occurred in the shell side. More than the 40% fluid flowed through the largest 20% void area of the total module void area (cells with high void fraction), and the smallest 20% void area (cell with low void fraction) carried less than 6% of the flow. This mal-distribution became more serious as the mean packing density increased.