The present invention relates to a method for preparing a transition metal complex for the preparation of an olefin copolymer, and more specifically, to a method for preparing a transition metal complex comprising: a transition metal of Group 4 in the periodic table; a cyclopentadienyl ligand; and at least one phenolic ligand capable of being purified by sublimation or a simple filtration, wherein a halogen, in particular chlorine, is not included in the preparation of the transition metal complex.