Propylene polymer and preparation method thereof

The invention provides a propylene polymer and a preparation method thereof. The method provided by the invention comprises the following steps: under first olefin gas-phase polymerization conditions, performing first contact reaction on a first part of propylene and a first part of hydrogen gas, and removing unreacted monomers and hydrogen gas from the mixture obtained through the first contact reaction, thus obtaining a first contact reaction product; and under second olefin gas-phase polymerization conditions, performing second contact reaction on the first contact reaction product, a second part of propylene, a second part of hydrogen gas and a comonomer, thus obtaining the propylene polymer, wherein an olefinic polymerization catalyst system contains an external electron donor compound, the external electron donor compound contains a first external electron donor compound selected from tetraethoxy silane and n-propyl trimethoxy silane and a second external electron donor compound selected from diisopropy