A multizone model is developed to analyze the reactants depletion phenomena in catalytic, slurry-phase olefin polymerization loop reactors. The modeling approach utilizes linking models at different length and time scales, namely, a kinetic model, a thermodynamic model and a reactor macroscopic model. In addition, a generalized population model equation is utilized to calculate the particle size distribution in the reactor. From the numerical solution of the proposed model, the spatial distribution of the reactants concentration, particle growth rate and particle size distribution in a catalytic polymerization loop reactor can be predicted. The model is further employed to assess the importance of using multifeed injection points along the reactor length for lessening the depletion phenomena and improving the product homogeneity. It is demonstrated that proper selection of the multifeed injection points of the reactants along the reactor length can significantly contribute in producing on-spec polymer grades with narrow particle size distribution.