Abstract: Salicylaldiminato neutral nickel(Ⅱ) complex and ［Ni(COD)2］ were prepared as catalyst system. The effects of polymerization processes on ethylene polymerization catalyzed by the neutral nickel(Ⅱ) complexes in toluene were studied in this work. The results show that the catalytic activity and molecular weight of polyethylene and tensile strength of polyethylene sheet enhance with increase of ethylene pressure and the agitation rate of polymerization. The polymerization activity and molecular weight of polyethylene reach maximum, and the more perfect crystal structure of polyethylene is achieved when the polymerization occurs at ambient temperature. The polyethylene obtained at ambient temperature has characterized by DSC, WAXD, GPC, dynamic rheology and mechanical tests. The results indicate that the polyethylene is linear and high molecular weight, and a little branched. The melting polyethylene behaves pseudoplasticity. The influence of ethylene pressure and stirring speed of polymerization on the crystal structure of the polyethylene obtained are small.