A dynamic model for ethylene copolymerization in an industrial Fluidized-Bed Reactor (FBR) is developed to describe its behavior and calculate the properties of polyethylene. The presented model considers particle entrainment and polymerization reaction in two phases. Two-site kinetic and hydrodynamic models in combination, provide a comprehensive model for the gas phase fluidized-bed polyethylene production reactor. The governing moment and hydrodynamic differential equations were solved simultaneously and the results compared with a similar work, as well as industrial data. The dynamic model showed accurate results for predicting Polydispersity Index (PDI), Molecular Weight Distribution (MWD), reactor temperature and polymer production rate. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.