The invention discloses an ethylene oligomerization reaction method; the method specifically comprises that water-containing ethylene is used as a raw material, and a complex chloro-2-acyl-1,10-phenanthroline amino-iron (II) represented by the formula (I) and used as a main catalyst, an aluminum-containing co-catalyst and an organic solvent are added; according to the method, an ethylene oligomerization reaction is carried out, the oligomerization reaction activity is high, the selectivity of alpha-olefin is high, the oligomerization reaction is fast to initiate, the operation is smooth and steady, and the repeatability is good; even when the aluminum/iron ratio is low, the catalyst still has good oligomerization reaction activity; therefore, the technical prejudice of technical personnel in the field is overcome, unexpected technical effects are obtained, and the catalytic effect and cost are better balanced, so that the cost of the ethylene oligomerization reaction is significantly decreased, the practicality is high, and the prospects for industrialization are broad.