The preparation of divalent chromium N-heterocyclic carbene(NHC,1,3-diisopropyl4,5-dimethylimidazole-2-ylidene)compounds is reported.The reaction of 1：1 molar ratio of NHC with CrCl2 led to an isolation of[(NHC)CrCl(μ-Cl)(THF)]2(1),while that of 2：1 ratio resulted in the formation of(NHC)2CrCl2(2).1 can be considered as an intermediate in the formation of 2 and further converted into 2 by the addition of another equiv.of NHC.The reaction of 2 with CpNa afforded an ion pair compound[(NHC)2CrCp]+[Cp]-(3),indicating a strong coordination ability of NHC supplanting one of the ionic Cr-Cp bonding.In combination of methylalumoxane(MAO)as cocatalyst 1 and 2 both are active for catalyzing ethylene polymerization.