A novel hyperbranched PNP chromium catalyst was synthesized using the materials of 1.0G hyperbranched macromolecule with hexylamine as core, chlorodiphenylphosphine and CrCl₃(THF)₃. The structure of the hyperbranched PNP chromium catalyst was fully characterized by IR, ¹H-NMR and UV. On the base of the synthesis of hyperbranched PNP chromium catalyst, the performance of ethylene oligomerization was investigated. The effects of the kind of solvent, reaction temperature, reaction pressure and Al/Cr ratio on catalytic performance in ethylene oligomerization were researched. The results show that the catalyst displays better catalytic performance in ethylene oligomerization with toluene as solvent and MAO as co-catalyst. The catalytic activity firstly increases and then decreases with the increase of reaction temperature and Al/Cr ratio. However, the catalytic activity increases with the increase of reaction pressure. The highest activity of 2.02×10^{4/sup>g/(mol Cr·h) and 92% selectivity of less than C₈ olefins are obtained under the conditions of the reaction temperature 35 ℃, the reaction pressure 1.0 MPa, and the Al/Cr ratio of 500. Under the same polymeric conditions, the catalytic activity of novel hyperbranched PNP chromium catalyst is better than the hyperbranched PNP chromium catalyst with a different length of alkyl chain in ethylene oligomerization.}