1-n-Butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6])/cyclohexane biphasic system was used for studying performance of ethylene oligomerization catalyzed by diphosphinoamine ligand (PNP)/Cr(Ⅲ)/ methylaluminoxane(MAO). The effect of reaction temperature

molar ratio of Al/Cr and ionic liquid concentration on catalytic activity and product distribution was investigated. The results showed that compared with homogeneous catalysis system

the action of catalytic active center in biphase systems changed from ethylene tetramerization to ethylene trimerization. selectivity was up to 97.40%. The product existed in the organic solvent while the catalyst was dissolved in ionic liquids

which made the separation of product and recycle of catalyst easy.