A novel Group IV elements-bridged metallocene complex is disclosed which is represented by the following formula (I): ##STR1## wherein R and R.sub.1 are different and are independently selected from the group consisting of .eta..sup.5 -cyclopentadienyl group, substituted .eta..sup.5 -cyclopentadienyl group, indenyl group, and fluorenyl group; R.sub.2 is selected from the group consisting of --N(CH.sub.3).sub.2, --N(C.sub.2 H.sub.5).sub.2, halogen, alkoxy, --(C.dbd.O)NH.sub.2, and C.sub.6-12 hydrocarbyl group; M is a Group IVA element; and M.sub.1 is a Group IVB metal. When employing the metallocene complex to prepare olefin polymers, since it is bridged by a Group IV element, there are two catalytic sites in the single metallocene complex catalyst. Therefore, the olefin monomers can be polymerized to a bimodal olefin polymer by a single catalyst in a single reactor, resulting in lowered capital costs.