The synthesis, characterization, and ethylene polymerization behavior of a novel macrocycle trinuclear 2,6-bis(imino)pyridyliron precatalyst 2 are reported. The molecular model of 2 was predicted using the Insight II software package. The molecular simulation indicates that the center iron atoms of complex 2 are located inside the macrocycle ligand. This new precatalyst could restrain active iron center from deactivation and effectively control chain transfer reaction, such as beta-H transfer to the metal or the monomer. Compared with its mononuclear analogue 1, precatalyst 2 shows higher activity and longer lifetime for ethylene polymerization in the presence of modified methylalumoxane as a cocatalyst and produces much higher molecular weight polyethylenes with higher melting temperatures. Furthermore, higher molecular weight polymers with unimodel molecular weight distribution can be easily obtained using triisobutylaluminum as a cocatalyst.