In this study, the half-metallocene was synthesized and then used in copolymerization of ethylene and 1-hexene with modified methyl aluminoxane as a cocatalyst. It was found from the investigation of comonomer effect that even thought the high amounts of comonomer were introduced into the half-metallocene catalytic systems, they were still in an active condition. From the comparative study on LLDPE/ silica composites synthesized by different copolymerization systems, it was found that the polymer composites can be efficiently produced by the half-metallocene catalytic systems especially combining with in situ impregnation methods. As regard the heterogeneous system, the support used can be modified by gallium to improve the activity for the system and the best method for preparation the supported catalysts was to mix between the catalyst and cocatalyst prior to immobilizing onto the support and then introducing it into the system. The most appropriate support for using in the catalytic system should have a spherical shape, a high surface area and a moderate pore diameter. Finally, from all the above investigations, a better understanding of the metallocene catalyst was achieved and the effective ways of using this catalyst in a certain condition were discovered.