The invention provides propene polymer and a preparation method thereof. The preparation method comprises the following steps of mixing a catalyst, a co-catalyst, an external donor, hydrogen and propene and performing first polymeric reaction to obtain a first product system which comprises first polymer; and mixing the first product system, hydrogen, propene, ethene and butane so that part of the first polymer, the hydrogen, the propene, the ethene and the butane are subjected to second polymeric reaction to obtain second polymer and then obtain propene polymer. The catalyst comprises at least one internal electron donor; and the co-catalyst is an organo-aluminum compound. The catalyst which comprises the efficient external electron donor and the internal electron donor can be used for preparing the propene polymer of a low dimethylbenzene soluble matter, and heat resistance and impact resistance of the propene polymer are improved. The second polymer which exists in the form of propene-ethene-bivinyl rubber has high heat resistance and impact resistance. The propene polymer has high impact resistance and high heat resistance.