This disclosure relates to a silica support for a metallocene catalyst used for olefin polymerization, a preparation method thereof, a metallocene catalyst using the same, and olefin polymer. Specifically, according to the present invention, a silica support used for preparing a metallocene supported catalyst is treated with a specific halogenized metal compound, thereby diversifying reaction sites to a cocatalyst when preparing a metallocene catalyst, and thus, the molecular weight distribution of produced olefin polymer may be much broadened and polymer having high molecular weight may be obtained compared to the existing support, even if the same metallocene catalyst is supported.