Fe(acac)(3)/2,6-bis[1-(2-isopropylanilinoethyl)] pyridine catalyst was immobilized on MCM-41 zeolite to synthesize ultrahigh molecular weight polyethylene (UHMWPE) with a weakly entangled state. Microstructure, Morphology, crystallization, and rheological properties of the nascent polyethylene were investigated by gel permeation chromatography, scanning electron microscope, differential scanning calorimetry, and rheometer, respectively. The polymer showed broad molecular weight distribution. We found that the synthesized UHMWPE had a weakly entangled state. The evolution of the weakly entangled state of the polymer was studied; however, it was found that the polymer synthesized in the initial stage of polymerization could be More entangled. Thus, poly[styrene-co-(acrylic acid)] (PS.) was coated on the surface of Cat-Fe/M to control the diffusion rate of ethylene, especially during the initial stage of polymerization. The decay rate of catalyst activity was decreased. The polymer synthesized at this stage then became more weakly entangled. The mechanism for achieving the weakly entangled state during polymerization was further discussed.