The invention discloses a catalyst composition used for an ethylene oligomerization reaction technology. The composition comprises a main catalyst 2-acetyl-6-(1H-2-benzoxazolyl)aminochloro iron (II) complex represented by formula (I), an aluminum-containing cocatalyst, water and an organic solvent. The catalyst composition prepared in the invention is used in the ethylene oligomerization reaction technology, has the advantages of very high oligomerization reaction activity, high selectivity of alpha-olefin, rapid initiation of the oligomerization reaction, stable running and good repeatability, still has very good oligomerization reaction activity even if the aluminum/iron ratio is low, so the technical prejudice of technical personnel in the field is overcome, an unexpected technical effect is achieved, and the catalysis effect and the cost are well balanced, thereby the ethylene oligomerization reaction cost is greatly reduced, the practicality is strong, and the industrial prospect is wide.