This invention relates to a transition metal half-metallocene catalyst that has unreactive structure and is used for preparing inter-isomorphism benzene vinyl polymer that has high activity, extremely excellent stereoregularity, high melting point and wide molecular weight distribution, and relates to a preparation of using this catalytic agent to prepare benzene vinyl polymer. This invention provides half-metallocene catalyst that has monocaryon structure, among them one side of transition metal that is in 3-10 subgroup in the periodic chart links with cyclane-diene group or 5-coordinate bond formed by derivation, besides the other side links with any one of trolamine, N-aldyl diolamine and N-Dialkyl ethanolamine which have many linking site and high steric hindrance. The unreactive metallocene catalyst of this invention is used to prepare hypso-inter-isomorphism vinyl- aromatic series polymer that has wide molecular weight distribution and high activity.