Abstract: A novel two-phase model for the fluidized bed of polyethylene with condensed mode operation was proposed.The model considered heat and mass conservation in emulsion phase and bubble phase, heat and mass transfer between emulsion phase and bubble phase,polymerization as well as resident time distribution of particles in emulsion phase.The relations between operating variables and reactor performance were investigated by the model.Simulation results agreed well with the industrial data.Simulation results indicate the productivity of reactor as well as ash in polymer will increase greatly, and low the temperature region will expand when the condensed mode is operating with the conventional catalyst.A type of catalyst which suits condensed mode operation was proposed.