The invention discloses a barrier polypropylene composition and a preparation method thereof, which relate to the preparation of a polypropylene composition. The barrier polypropylene composition comprises the following components in part by weight: 100 parts of polypropylene resin (in terms of polypropylene), 0.01 to 1 part (preferably 0.03 to 0.5 part) of beta nucleating agent, 0.1 to 4 parts (preferably 0.2 to 2 parts) of nano silicon dioxide, 0.1 to 2 parts of maleic anhydride grafted polypropylene serving as a compatilizer, and other processing assistant. The barrier polypropylene composition and the preparation method of the invention are economic; the barrier property of the polypropylene composition can be improved obviously by simply adding a small amount of other substances; andthe barrier polypropylene composition is applicable in packaging industries having barrier and sanitation requirements, such as medicine and food package industries.