The invention relates to a catalyst used for olefin polymerization and a preparation method thereof. The preparation method is as follows: in a reactor, under the protection of nitrogen, adding an organic solvent and a titanium compound, cooling to-30 to-10 DEG C, adding a carrier, maintaining at-30 to-10 DEG C, and stirring for 30-40min; slowly heating to 100 to 120 DEG C, in the heating process, adding an electron donor compound, reacting at 100-120 DEG C for 30-40min, filtering a liquid, again adding the titanium compound, heating to 110 to 130 DEG C, maintaining at 110 to 130 DEG C for 30-40min, filtering the liquid, washing an obtained solid, and drying under vacuum to obtain a target product. In a magnesium halide alcohol adduct formation process, a forming agent and a particle form control agent are added, the particle size distribution of the obtained carrier is more concentrated, the carrier is used for preparing the catalyst, activity and hydrogen sensitivity of the catalyst can be improved when the carrier is used for olefin polymerization especially for propylene polymerization, the bulk density of an obtained polymerization product is moderate, and the polymerization product is basically free of abnormity materials.