Disclosed is a multinuclear transition metal half metallocene catalyst having a multinuclear half metallocene structure in which a transition metal of groups 3 to 10 on periodic table is connected to a cycloalkandienyl group or its derivative group on a side and also connected to phenol or phenolamine compound having a plurality of binding sites on another side. The metallocene catalyst is useful to produce syndiotatic styrene polymer having superior steroreguality, high melting point and broad molecular weight distribution with high activity together with a small amount of a cocatalyst. Further disclosed is a method for preparing styrene polymers using the same catalyst.