Olefin polymer and preparation method thereof

The invention relates to an olefin polymer and a preparation method thereof. According to the method, an olefin polymerization catalyst system comes into contact with one or more olefins under the condition of olefin polymerization, wherein the olefin polymerization catalyst system contains a solid component, an external electron donor compound and an organic aluminum compound, the solid component contains titanium, magnesium and an internal electron donor compound, the external electron donor compound contains a first external electron donor compound and a second external electron donor compound, the first external electron donor compound is diisobutyldimethoxysilane and the second external electron donor compound is n-propyl trimethoxysilane and/or tetraethoxy-silicone. The olefin polymerization method provided by the invention has excellent hydrogen regulation sensibility and high polymerization efficiency and is applicable to occasions of preparation of propene polymers in a gaseous polymerization way.