The present invention relates to a preparation method of a metallocene catalyst. More particularly, the present invention relates to a preparation method of a supported hybrid metallocene catalyst, including the steps of treating a support having a water content of 4 to 7% by weight with trialkyl aluminum at a predetermined temperature; supporting alkyl aluminoxane on the support; and supporting a metallocene compound on the alkyl aluminoxane-supported support. According to the present invention, it is possible to prepare a supported hybrid metallocene catalyst which shows a high activity in the polymerization of olefins and enables the preparation of polyolefins having a high bulk density, by a simple process.